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blue · cool

#3f4dbb

a balanced, vivid blue · cool · closest name: Slate Blue

Token name suggestion: Atlas Cobalt

RGB
63, 77, 187
HSL
233°, 50%, 49%
CMYK
66, 59, 0, 27
Luminance
0.0995

#3f4dbb is a balanced vivid blue, 233° on the wheel and 87/100 on the cool side. Put white text on it (7.02:1). As text it scores 7.02:1 on white — safe at any size. Nearest name is Slate Blue, nearest Tailwind family is indigo.

hsl(233 50% 49%)rgb(63 77 187)Base step 600AAA inkCool

At a glance

Every number on this page in one read: what #3f4dbb is made of, how bright it looks, and which way it leans.

Hex
#3f4dbb
Hue
233°
blue
Saturation
50%
vivid
Lightness
49%
balanced
Brightness
73%
HSV value
Perceived
36%
weighted brightness
Luminance
0.0995
WCAG relative
Temperature
Cool
87/100 cool
Color family
Blue
Tone
Vivid
Best ink
White
7.02:1
Closest name
Slate Blue
ΔE2000 7.9
Chroma
67.0
LCH, 0–130ish
OKLCH L
0.475
perceptual lightness
Tailwind
indigo
500 · ΔE 11.8
Web-safe
#3366CC
nearest of 216
Where it sits
Hue233° of 360°
Saturation50%
Lightness49%
Saturation × lightness field

Left edge is grey, right edge is full chroma; top is white, bottom is black. The dot is #3f4dbb.

Temperature
Warm ← → Cool87% cool

Reads cool. Warm and cool siblings keep the same lightness, so you can swap one in without redoing your contrast maths.

Luminance by channel
Red11%
Green53%
Blue36%

Green carries most of what the eye calls brightness — that is why WCAG weights it 0.7152.

Every format

HEX#3f4dbb
HEX (8-digit)#3f4dbbff
RGBrgb(63, 77, 187)
RGBArgba(63, 77, 187, 1)
HSLhsl(233, 50%, 49%)
HSV / HSBhsv(233, 66%, 73%)
HWBhwb(233 25% 27%)
CMYKcmyk(66%, 59%, 0%, 27%)
LABlab(37.8 30.3 -59.8)
LCHlch(37.8 67.0 296.9)
OKLCHoklch(0.475 0.172 272.5)
XYZ (D65)xyz(13.67, 9.95, 48.20)
Decimal4148667
Display P3color(display-p3 0.247 0.302 0.733)
Web-safe#3366CC

Copy-ready code

every platformclick to select
/* CSS */
color: #3f4dbb;
background-color: #3f4dbb;
/* CSS custom property */
--brand: #3f4dbb;
/* Tailwind (arbitrary) */
class="text-[#3f4dbb] bg-[#3f4dbb]"
/* SCSS */
$brand: #3f4dbb;
/* SwiftUI */
Color(red: 0.247, green: 0.302, blue: 0.733)
/* UIKit */
UIColor(red: 0.247, green: 0.302, blue: 0.733, alpha: 1)
/* Android XML */
<color name="brand">#3F4DBB</color>
/* Android Compose */
Color(0xFF3F4DBB)
/* Flutter */
Color(0xFF3F4DBB)
/* Python / OpenCV (BGR) */
(187, 77, 63)
/* Python / PIL (RGB) */
(63, 77, 187)
/* Java AWT */
new Color(63, 77, 187)
/* .NET */
Color.FromArgb(255, 63, 77, 187)
/* OpenGL / Unity (0–1) */
(0.2471f, 0.3020f, 0.7333f, 1f)
/* LaTeX */
\definecolor{brand}{RGB}{63,77,187}
modern cssclick to select
/* mix without leaving CSS */
background: color-mix(in oklab, #3f4dbb 85%, white);
border-color: color-mix(in oklab, #3f4dbb 40%, transparent);
/* theme-aware in one line */
color: light-dark(#20275F, #D3D6EE);
/* relative colour syntax */
--hover: hsl(from #3f4dbb h s calc(l - 7));

Design tokens

The same ramp in the four formats a team actually needs. Paste one and the whole palette lands with it.

css custom propertiesclick to select
:root {
  --brand-50: #F4F5FA;
  --brand-100: #EAEBF6;
  --brand-200: #CFD3EC;
  --brand-300: #ABB1E3;
  --brand-400: #818BD5;
  --brand-500: #5764C6;
  --brand-600: #3f4dbb;
  --brand-700: #333F99;
  --brand-800: #29327A;
  --brand-900: #212859;
  --brand-950: #151938;
  --brand: #3f4dbb;
  --brand-ink: #ffffff;
  --brand-surface: #F4F5FA;
  --brand-border: #C2C7EA;
  --brand-hover: #3642A0;
  --brand-pressed: #2D3786;
}
@media (prefers-color-scheme: dark) {
  :root {
    --brand-surface: #141624;
    --brand-ink: #D3D6EE;
  }
}
tailwind.config.jsclick to select
theme: {
  extend: {
    colors: {
      brand: {
        50: '#F4F5FA',
        100: '#EAEBF6',
        200: '#CFD3EC',
        300: '#ABB1E3',
        400: '#818BD5',
        500: '#5764C6',
        600: '#3f4dbb',
        700: '#333F99',
        800: '#29327A',
        900: '#212859',
        950: '#151938',
        DEFAULT: '#3f4dbb',
      },
    },
  },
}
scss mapclick to select
$brand: (
  '50': #F4F5FA,
  '100': #EAEBF6,
  '200': #CFD3EC,
  '300': #ABB1E3,
  '400': #818BD5,
  '500': #5764C6,
  '600': #3f4dbb,
  '700': #333F99,
  '800': #29327A,
  '900': #212859,
  '950': #151938,
);
$brand-base: #3f4dbb;
$brand-ink: #ffffff;

@function brand($step) { @return map-get($brand, $step); }
w3c design tokens (json)click to select
{
  "color": {
    "brand": {
      "50": { "$value": "#F4F5FA", "$type": "color" },
      "100": { "$value": "#EAEBF6", "$type": "color" },
      "200": { "$value": "#CFD3EC", "$type": "color" },
      "300": { "$value": "#ABB1E3", "$type": "color" },
      "400": { "$value": "#818BD5", "$type": "color" },
      "500": { "$value": "#5764C6", "$type": "color" },
      "600": { "$value": "#3f4dbb", "$type": "color" },
      "700": { "$value": "#333F99", "$type": "color" },
      "800": { "$value": "#29327A", "$type": "color" },
      "900": { "$value": "#212859", "$type": "color" },
      "950": { "$value": "#151938", "$type": "color" }
    },
    "brandInk": { "$value": "#ffffff", "$type": "color" }
  }
}

Best text color

Only one of black and white can be right. This is the one, with the number that proves it.

Readable at a glance#ffffff on #3f4dbb · 7.02:1
Use #ffffffAAA at every size.
Aa
12px
Aa
16px
Aa
24px
Aa
White text · 7.02:1 · recommended
AA pass · AA large pass · AAA pass
Aa
Black text · 2.99:1
AA fail · AA large fail · AAA fail
Reading the other direction: #3f4dbb as text scores 7.02:1 on white and 2.99:1 on black.
Best tinted ink on it, if plain black or white feels flat: #ECEDF9 at 6.04:1.

Make it accessible

A contrast checker tells you that you failed. This tells you what to ship instead — same hue, same saturation, lightness moved only as far as WCAG demands.

The quick fox
#3f4dbb · 7.02:1
AA on whitealready passes
#3f4dbb
The quick fox
#3f4dbb · 7.02:1
AAA on whitealready passes
#3f4dbb
The quick fox
#636ECA · 4.61:1
AA on black+10% L
#636ECA
The quick fox
#8992D7 · 7.16:1
AAA on black+20% L
#8992D7

Large text — 24px regular or 18.66px bold and above — only needs 3:1, so #3F4DBB is enough for headings on white. Non-text elements such as icons, chart strokes and focus rings also sit at 3:1 under WCAG 2.2 (1.4.11).

Accessibility — WCAG contrast

Aa
#3f4dbb on white: 7.02:1
AA ✓ pass · AA-large · AAA
Aa
#3f4dbb on black: 2.99:1
AA ✗ fail · AA-large · AAA
Against the neutral ladder

Contrast is symmetric, so each row covers both directions: #3f4dbb as text on that neutral, and that neutral as text on #3f4dbb.

NeutralRatioBoth directions
White7.02:1AaAa
Slate 506.71:1AaAa
Slate 1006.41:1AaAa
Slate 2005.70:1AaAa
Slate 3004.73:1AaAa
Slate 4002.74:1AaAa
Slate 5001.48:1AaAa
Slate 6001.08:1AaAa
Slate 7001.47:1AaAa
Slate 8002.08:1AaAa
Slate 9002.54:1AaAa
Black2.99:1AaAa
Colour vision deficiency
true color
protanopia · #005FBF
deuteranopia · #0053B9
tritanopia · #00687C

Roughly one man in twelve has some form of colour vision deficiency. If any of the three panels above is hard to tell apart from a neighbouring colour in your palette, add a shape, an icon or a label so the meaning does not rest on hue alone.

Color scale — 50 to 950

A Tailwind-shaped ramp built around this exact hex. #3f4dbb is pinned to step 600; the rest hold its hue and let saturation ease off at the extremes so the pale end never turns neon.

#F4F5FA
#EAEBF6
#CFD3EC
#ABB1E3
#818BD5
#5764C6
#3f4dbb
#333F99
#29327A
#212859
#151938
Base = 600Lightest = 50 · #F4F5FADarkest = 950 · #151938Text step on white = 500
Perceptual ramp — OKLCH

The same eleven steps expressed in OKLCH, where equal lightness numbers actually look equally spaced. HSL ramps go muddy in the yellows and washed out in the blues; this one does not. Modern browsers render it natively — the hex ramp above is the fallback.

50100200300400500600700800900950
oklch tokensclick to select
:root {
  --brand-50: oklch(0.97 0.043 272.5);
  --brand-100: oklch(0.94 0.069 272.5);
  --brand-200: oklch(0.88 0.103 272.5);
  --brand-300: oklch(0.80 0.134 272.5);
  --brand-400: oklch(0.72 0.158 272.5);
  --brand-500: oklch(0.64 0.172 272.5);
  --brand-600: oklch(0.56 0.172 272.5);
  --brand-700: oklch(0.48 0.162 272.5);
  --brand-800: oklch(0.40 0.145 272.5);
  --brand-900: oklch(0.32 0.121 272.5);
  --brand-950: oklch(0.24 0.095 272.5);
}

Colors that work with #3f4dbb

Not a palette — a role sheet. Each swatch answers one question you will hit while building the component.

Text on it#ffffff
White wins here
Surface#F4F5FA
Tinted page background
Border#C2C7EA
Hairlines and dividers
Muted text#4B549B
Captions on the surface
Accent#9D752F
Second voice, not a rival
Dark variant#20275F
Hover, pressed, headers
Light variant#ECEDF9
Selected rows, tints
Dark surface#141624
Dark-mode background
Hover#3642A0
One step down in lightness
Pressed#2D3786
Two steps down
Disabled#A5A8C5
Chroma pulled out
Focus ring#4050CF
Offset from the fill so it reads
Light mode
Everything in its place

Surface, border, heading and body all derive from this one hue, so the screen stays coherent without a second palette.

Primary actionSecondaryBadge
Dark mode
Same hue, inverted

Lightness flips, hue holds. The accent stays the anchor in both themes.

Primary actionSecondaryAccent

In real components

The same eight roles, wired into the interface patterns you will actually build with them. Every state below is a computed value, not a mock-up.

Buttons and states
Save changesHoverPressedDisabled
OutlineSubtleLinkFocused
Form field
you@company.com

Focus ring uses the light variant so the field still reads as one shape.

Send me product updates
Notice
Your export is ready

The file stays available for seven days. Download it before it expires.

NewBetaDraft
Data
Storage used68%
Acme LtdActive
NorthwindTrial
GlobexActive

How to use #3f4dbb

Derived from its contrast, chroma and lightness — not from taste.

Works well for
  • Body text and links on white
  • Primary buttons and calls to action
  • Focus rings, active and selected states
  • Brand accents, badges and data highlights
  • Chart series and data categories
Use with care
  • Text on black or near-black surfaces
  • Full-page backgrounds — tiring over long sessions
  • Pairing with a same-lightness hue — edges vibrate
Minimum size as text on white
Any size
Safe as a fill behind white type
Yes
Safe as a 1px border on white
Yes

Meaning and mood

What a colour in this family tends to signal, and how this particular chroma and lightness change the reading.

trustedcalmcompetentcorporate

The default of institutions for a reason: blue is read as stable and safe across nearly every culture that has been surveyed.

This is a confident chroma: strong enough to lead a brand, restrained enough to live in an interface all day. The mid lightness keeps it versatile in both themes.

Worth knowing

It is also the most crowded hue on the web. Distinctiveness has to come from your other choices.

Reads as
  • FormalityMedium
  • EnergyMedium-high
  • Weight51/100
  • TemperatureCool
  • ApproachabilityReserved

Colour associations are cultural and vary by market. Treat these as a starting point for a conversation with your audience, not a finding about them.

Similar colors

One move away from this hex in each direction. Every swatch is its own page.

Color relationships

The wheel positions with their names attached, so you can grab the one you actually need.

Complementary#BBAD3F
Analogous left#3F8BBB
Analogous right#6F3FBB
Split-complement 1#BB6F3F
Split-complement 2#8BBB3F
Triadic 1#BB3F4D
Triadic 2#4DBB3F
Tetradic#BB3F8B
On the wheel
Base+30°−30°+120°+240°+180°233°

#3f4dbb sits at 233°. Every dot is a harmony position and links to its own page in the table alongside.

RGB percentages

Red24.7%
Green30.2%
Blue73.3%
R · 0–255
63
0x3f
G · 0–255
77
0x4d
B · 0–255
187
0xbb

CMYK percentages

Cyan66.3%
Magenta58.8%
Yellow0.0%
Key (black)26.7%

Total ink coverage is 152%. Most commercial presses cap around 300% — above that, sheets stop drying properly.

Color previews

#3f4dbb text on a black background

contrast 2.99:1

Card sample

#3f4dbb text on a white background

contrast 7.02:1

Card sample

#3f4dbb on grey

6.41:1

#3f4dbb on its own surface

6.45:1

#3f4dbb on its dark surface

2.56:1

CSS3 live lab

Text font color

The quick brown fox

color: #3f4dbb;
Background color
Panel with #3f4dbb background
background-color: #3f4dbb;
Text shadow — hex

Glowing headline

text-shadow: 2px 2px 8px #3f4dbb;
Text shadow — RGB

Soft neon halo

text-shadow: 0 0 14px rgba(63, 77, 187, 0.45);
Div box shadow
Elevated card
box-shadow: 0 12px 32px -8px rgba(63, 77, 187, 0.45);
Border & gradient
Gradient panel
border: 3px solid #3f4dbb;
background: linear-gradient(135deg, #3f4dbb, #843FBB);
Gradient text

Gradient headline

background: linear-gradient(90deg, #3f4dbb, #A33FBB);
-webkit-background-clip: text;
color: transparent;
Focus ring
Focused control
outline: 2px solid #3f4dbb;
outline-offset: 3px;
Underline & caret

Marked up text

text-decoration-color: #3f4dbb;
caret-color: #3f4dbb;
Left rule
Pull quote or callout
border-left: 4px solid #3f4dbb;
Ring + tint
Selected chip
background: #ECEDF9;
box-shadow: inset 0 0 0 2px #3f4dbb;
Conic badge
68%
background: conic-gradient(#3f4dbb 68%, #e2e8f0 0);

Transparency

What each alpha value actually composites to. The top row is #3f4dbb over white; the bottom row is the same alpha over a checkerboard, so you can see what survives on a photo or a video.

Bottom row of hexes is the flattened result over white — use those when a design tool refuses transparency, or when you need a solid fallback.

alpha in every syntaxclick to select
rgba(63, 77, 187, 0.5)
rgb(63 77 187 / 50%)
#3f4dbb80
hsl(233 50% 49% / 50%)
color-mix(in srgb, #3f4dbb 50%, transparent)
Alpha8-digit hexFlat on white
10%#3f4dbb1a#ECEDF8
20%#3f4dbb33#D9DBF1
40%#3f4dbb66#B2B8E4
60%#3f4dbb99#8C94D6
80%#3f4dbbcc#6571C9

Gradients from #3f4dbb

Six recipes, each built from this hex and shown with the exact CSS that produced it.

Elevation
Same hue, three lightnesses — safe anywhere
background: linear-gradient(135deg, #6A75CD, #3f4dbb 45%, #20275F);
Duotone
A short hue run reads richer than a flat fill
background: linear-gradient(120deg, #3f4dbb, #7D37A4);
Complement sweep
Loud — keep it behind large type only
background: linear-gradient(90deg, #3f4dbb, #BBAD3F);
Spotlight
Hero panels and app headers
background: radial-gradient(120% 120% at 20% 0%, #818BD5 0%, #3f4dbb 45%, #20275F 100%);
Soft wash
Section backgrounds that stay readable
background: linear-gradient(180deg, #F4F5FA, #ffffff);
Mesh
Ambient background, no image weight
background: radial-gradient(60% 60% at 15% 20%, #63ABCA 0%, transparent 60%), radial-gradient(55% 55% at 85% 15%, #8953C5 0%, transparent 60%), radial-gradient(70% 70% at 50% 95%, #20275F 0%, transparent 65%), #3f4dbb;

Monochromatic scale

Palettes built from #3f4dbb

Shades — darker

Tints — lighter

Tones — desaturated

Color harmonies

Nearest named colors

Ranked with CIEDE2000 across all 139 CSS keywords. Under ΔE 2 the eye stops telling them apart; over ΔE 10 they are plainly different colors.

#3f4dbb in the real world

Where a color in this family tends to land, and the interface roles it is usually asked to play.

Industries
TechnologyFinanceHealthcareEnterprise SaaS
Common UI roles
ButtonsLinksFocus statesCharts
Print note

Converts to four-color process without much drama. Proof it anyway.

On screens

Holds up across typical panel gamma. Still worth checking on an uncalibrated laptop, where mid-tones shift most.

In dark mode

Too dim on dark surfaces at 2.99:1 — lift it to #636ECA for body text, or reserve it for fills.

Explore nearby colors

Small, deliberate steps away from this hex — useful when you are hunting for the version of a colour that finally feels right.

#3f4dbb, answered

What color is #3f4dbb?

#3f4dbb is a balanced vivid blue, closest to Slate Blue (ΔE2000 7.9). It sits at 233° on the hue wheel with 50% saturation and 49% lightness, which reads as cool.

What is the RGB value of #3f4dbb?

rgb(63, 77, 187) — 63 red, 77 green and 187 blue out of 255, or 24.7% / 30.2% / 73.3% by channel.

What is #3f4dbb in HSL and HSV?

hsl(233, 50%, 49%) and hsv(233, 66%, 73%). HSL is what CSS takes; HSV is what your design tool's picker shows, which is why the saturation numbers rarely match.

Is #3f4dbb a light or a dark color?

It is a dark color. Relative luminance is 0.0995 and perceived brightness is 36%, so white text on it reaches 7.02:1.

Should I use black or white text on #3f4dbb?

White. It scores 7.02:1 against #3f4dbb, versus 2.99:1 for black — AAA at any size.

Is #3f4dbb accessible on a white background?

#3f4dbb on white scores 7.02:1, which clears AAA at every size.

What is the complementary color of #3f4dbb?

#BBAD3F sits directly opposite on the wheel. Softer options are the split-complements #BB6F3F and #8BBB3F, which give the same contrast with far less vibration.

What colors go well with #3f4dbb?

For interface work: #F4F5FA as the surface, #C2C7EA for borders, #4B549B for secondary text, #9D752F as an accent and #20275F for hover and pressed states. For a palette, the analogous pair #3F8BBB and #6F3FBB stays calm, while #BBAD3F is the loudest partner.

What is #3f4dbb in CMYK for printing?

cmyk(66%, 59%, 0%, 27%). This is a screen-to-ink approximation — ask your printer for a proof before committing to a run.

Is #3f4dbb warm or cool?

Cool — it scores 87 on a scale where 0 is the warmest orange and 100 the coolest azure. Nudged warmer it becomes #5E3FBB; nudged cooler, #3C67BD.

Which Tailwind color is closest to #3f4dbb?

The indigo family — its 500 step is #6366f1, ΔE2000 11.8 away. That is a visible difference, so define #3f4dbb as a custom token rather than reaching for the built-in.

How do I use #3f4dbb in Tailwind CSS?

Inline it as an arbitrary value with bg-[#3f4dbb] or text-[#3f4dbb], or register the whole ramp under theme.extend.colors.brand so you get bg-brand-500 and friends. The generated 50–950 scale on this page is ready to paste into your config.

What is #3f4dbb with 50% opacity?

rgba(63, 77, 187, 0.5), or #3f4dbb80 in eight-digit hex. Over white that composites to #9FA6DD; over black, #20275E.

Is #3f4dbb a web-safe color?

No. The nearest web-safe colour is #3366CC, ΔE2000 9.2 away. The palette only matters for legacy displays and some email clients now.

What does the color #3f4dbb mean?

As a blue, it reads trusted, calm, competent. The default of institutions for a reason: blue is read as stable and safe across nearly every culture that has been surveyed. At this chroma the effect is amplified — it will dominate whatever sits beside it.

What gradient works with #3f4dbb?

The safest is same-hue elevation: linear-gradient(135deg, #6A75CD, #3f4dbb 45%, #20275F). For more colour, a short hue run to #7D37A4 keeps it rich without turning muddy.

Work with #3f4dbb in the Color Lab

Every tool opens with this colour already loaded.

Every value on this page is computed from #3f4dbb at request time — conversions, contrast ratios and ΔE distances are calculated, never looked up.