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blue · cool

#645b8c

a balanced, soft blue · cool · closest name: Dark Slate Blue

Token name suggestion: True Sapphire

RGB
100, 91, 140
HSL
251°, 21%, 45%
CMYK
29, 35, 0, 45
Luminance
0.1208

#645b8c is a balanced soft blue, 251° on the wheel and 66/100 on the cool side. Put white text on it (6.15:1). As text it scores 6.15:1 on white — safe at any size. Nearest name is Dark Slate Blue, nearest Tailwind family is slate.

hsl(251 21% 45%)rgb(100 91 140)Base step 600AA inkCool

At a glance

Every number on this page in one read: what #645b8c is made of, how bright it looks, and which way it leans.

Hex
#645b8c
Hue
251°
blue
Saturation
21%
soft
Lightness
45%
balanced
Brightness
55%
HSV value
Perceived
39%
weighted brightness
Luminance
0.1208
WCAG relative
Temperature
Cool
66/100 cool
Color family
Blue
Tone
Soft
Best ink
White
6.15:1
Closest name
Dark Slate Blue
ΔE2000 11.1
Chroma
30.0
LCH, 0–130ish
OKLCH L
0.500
perceptual lightness
Tailwind
slate
500 · ΔE 13.1
Web-safe
#666699
nearest of 216
Where it sits
Hue251° of 360°
Saturation21%
Lightness45%
Saturation × lightness field

Left edge is grey, right edge is full chroma; top is white, bottom is black. The dot is #645b8c.

Temperature
Warm ← → Cool66% 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
Red22%
Green62%
Blue16%

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

Every format

HEX#645b8c
HEX (8-digit)#645b8cff
RGBrgb(100, 91, 140)
RGBArgba(100, 91, 140, 1)
HSLhsl(251, 21%, 45%)
HSV / HSBhsv(251, 35%, 55%)
HWBhwb(251 36% 45%)
CMYKcmyk(29%, 35%, 0%, 45%)
LABlab(41.4 15.1 -25.9)
LCHlch(41.4 30.0 300.3)
OKLCHoklch(0.500 0.077 291.8)
XYZ (D65)xyz(13.73, 12.08, 26.42)
Decimal6577036
Display P3color(display-p3 0.392 0.357 0.549)
Web-safe#666699

Copy-ready code

every platformclick to select
/* CSS */
color: #645b8c;
background-color: #645b8c;
/* CSS custom property */
--brand: #645b8c;
/* Tailwind (arbitrary) */
class="text-[#645b8c] bg-[#645b8c]"
/* SCSS */
$brand: #645b8c;
/* SwiftUI */
Color(red: 0.392, green: 0.357, blue: 0.549)
/* UIKit */
UIColor(red: 0.392, green: 0.357, blue: 0.549, alpha: 1)
/* Android XML */
<color name="brand">#645B8C</color>
/* Android Compose */
Color(0xFF645B8C)
/* Flutter */
Color(0xFF645B8C)
/* Python / OpenCV (BGR) */
(140, 91, 100)
/* Python / PIL (RGB) */
(100, 91, 140)
/* Java AWT */
new Color(100, 91, 140)
/* .NET */
Color.FromArgb(255, 100, 91, 140)
/* OpenGL / Unity (0–1) */
(0.3922f, 0.3569f, 0.5490f, 1f)
/* LaTeX */
\definecolor{brand}{RGB}{100,91,140}
modern cssclick to select
/* mix without leaving CSS */
background: color-mix(in oklab, #645b8c 85%, white);
border-color: color-mix(in oklab, #645b8c 40%, transparent);
/* theme-aware in one line */
color: light-dark(#37324D, #DCDAE7);
/* relative colour syntax */
--hover: hsl(from #645b8c 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: #F7F6F9;
  --brand-100: #EEEDF2;
  --brand-200: #DAD8E4;
  --brand-300: #BFBBD3;
  --brand-400: #A099BD;
  --brand-500: #8077A7;
  --brand-600: #645b8c;
  --brand-700: #58507C;
  --brand-800: #474063;
  --brand-900: #363149;
  --brand-950: #221F2E;
  --brand: #645b8c;
  --brand-ink: #ffffff;
  --brand-surface: #F6F6F9;
  --brand-border: #D1CEDF;
  --brand-hover: #554D76;
  --brand-pressed: #453F61;
}
@media (prefers-color-scheme: dark) {
  :root {
    --brand-surface: #181622;
    --brand-ink: #DCDAE7;
  }
}
tailwind.config.jsclick to select
theme: {
  extend: {
    colors: {
      brand: {
        50: '#F7F6F9',
        100: '#EEEDF2',
        200: '#DAD8E4',
        300: '#BFBBD3',
        400: '#A099BD',
        500: '#8077A7',
        600: '#645b8c',
        700: '#58507C',
        800: '#474063',
        900: '#363149',
        950: '#221F2E',
        DEFAULT: '#645b8c',
      },
    },
  },
}
scss mapclick to select
$brand: (
  '50': #F7F6F9,
  '100': #EEEDF2,
  '200': #DAD8E4,
  '300': #BFBBD3,
  '400': #A099BD,
  '500': #8077A7,
  '600': #645b8c,
  '700': #58507C,
  '800': #474063,
  '900': #363149,
  '950': #221F2E,
);
$brand-base: #645b8c;
$brand-ink: #ffffff;

@function brand($step) { @return map-get($brand, $step); }
w3c design tokens (json)click to select
{
  "color": {
    "brand": {
      "50": { "$value": "#F7F6F9", "$type": "color" },
      "100": { "$value": "#EEEDF2", "$type": "color" },
      "200": { "$value": "#DAD8E4", "$type": "color" },
      "300": { "$value": "#BFBBD3", "$type": "color" },
      "400": { "$value": "#A099BD", "$type": "color" },
      "500": { "$value": "#8077A7", "$type": "color" },
      "600": { "$value": "#645b8c", "$type": "color" },
      "700": { "$value": "#58507C", "$type": "color" },
      "800": { "$value": "#474063", "$type": "color" },
      "900": { "$value": "#363149", "$type": "color" },
      "950": { "$value": "#221F2E", "$type": "color" }
    },
    "brandInk": { "$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 #645b8c · 6.15:1
Use #ffffffAA at every size, AAA for large text only.
Aa
12px
Aa
16px
Aa
24px
Aa
White text · 6.15:1 · recommended
AA pass · AA large pass · AAA fail
Aa
Black text · 3.42:1
AA fail · AA large pass · AAA fail
Reading the other direction: #645b8c as text scores 6.15:1 on white and 3.42:1 on black.
Best tinted ink on it, if plain black or white feels flat: #F1F0F5 at 5.42:1.

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
#645b8c · 6.15:1
AA on whitealready passes
#645b8c
The quick fox
#5B5380 · 7.01:1
AAA on white−4% L
#5B5380
The quick fox
#786FA1 · 4.59:1
AA on black+8% L
#786FA1
The quick fox
#9891B7 · 7.07:1
AAA on black+19% L
#9891B7

Large text — 24px regular or 18.66px bold and above — only needs 3:1, so #645B8C 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
#645b8c on white: 6.15:1
AA ✓ pass · AA-large · AAA
Aa
#645b8c on black: 3.42:1
AA ✗ fail · AA-large · AAA
Against the neutral ladder

Contrast is symmetric, so each row covers both directions: #645b8c as text on that neutral, and that neutral as text on #645b8c.

NeutralRatioBoth directions
White6.15:1AaAa
Slate 505.87:1AaAa
Slate 1005.61:1AaAa
Slate 2004.99:1AaAa
Slate 3004.14:1AaAa
Slate 4002.40:1AaAa
Slate 5001.29:1AaAa
Slate 6001.23:1AaAa
Slate 7001.68:1AaAa
Slate 8002.38:1AaAa
Slate 9002.90:1AaAa
Black3.42:1AaAa
Colour vision deficiency
true color
protanopia · #4E628E
deuteranopia · #4E618B
tritanopia · #5B636D

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. #645b8c 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.

#F7F6F9
#EEEDF2
#DAD8E4
#BFBBD3
#A099BD
#8077A7
#645b8c
#58507C
#474063
#363149
#221F2E
Base = 600Lightest = 50 · #F7F6F9Darkest = 950 · #221F2EText step on white = 600
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 0.019 291.8);
  --brand-100: oklch(0.94 0.031 291.8);
  --brand-200: oklch(0.88 0.046 291.8);
  --brand-300: oklch(0.80 0.060 291.8);
  --brand-400: oklch(0.72 0.071 291.8);
  --brand-500: oklch(0.64 0.077 291.8);
  --brand-600: oklch(0.56 0.077 291.8);
  --brand-700: oklch(0.48 0.073 291.8);
  --brand-800: oklch(0.40 0.065 291.8);
  --brand-900: oklch(0.32 0.054 291.8);
  --brand-950: oklch(0.24 0.043 291.8);
}

Colors that work with #645b8c

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#F6F6F9
Tinted page background
Border#D1CEDF
Hairlines and dividers
Muted text#635A8B
Captions on the surface
Accent#918D56
Second voice, not a rival
Dark variant#37324D
Hover, pressed, headers
Light variant#F1F0F5
Selected rows, tints
Dark surface#181622
Dark-mode background
Hover#554D76
One step down in lightness
Pressed#453F61
Two steps down
Disabled#A09ABD
Chroma pulled out
Focus ring#6556A5
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 #645b8c

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

Works well for
  • Body text and links on white
  • Charts, tags and secondary surfaces
  • Brand accents, badges and data highlights
  • Chart series and data categories
Use with care
  • 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.

The muted chroma softens the association — it reads considered rather than loud, which suits long-form and data-heavy screens. 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
  • Weight55/100
  • 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#838C5B
Analogous left#5B6B8C
Analogous right#7C5B8C
Split-complement 1#8C7C5B
Split-complement 2#6B8C5B
Triadic 1#8C645B
Triadic 2#5B8C64
Tetradic#8C5B6B
On the wheel
Base+30°−30°+120°+240°+180°251°

#645b8c sits at 251°. Every dot is a harmony position and links to its own page in the table alongside.

RGB percentages

Red39.2%
Green35.7%
Blue54.9%
R · 0–255
100
0x64
G · 0–255
91
0x5b
B · 0–255
140
0x8c

CMYK percentages

Cyan28.6%
Magenta35.0%
Yellow0.0%
Key (black)45.1%

Total ink coverage is 109%. Most commercial presses cap around 300% — above that, sheets stop drying properly.

Color previews

#645b8c text on a black background

contrast 3.42:1

Card sample

#645b8c text on a white background

contrast 6.15:1

Card sample

#645b8c on grey

5.61:1

#645b8c on its own surface

5.70:1

#645b8c on its dark surface

2.90:1

CSS3 live lab

Text font color

The quick brown fox

color: #645b8c;
Background color
Panel with #645b8c background
background-color: #645b8c;
Text shadow — hex

Glowing headline

text-shadow: 2px 2px 8px #645b8c;
Text shadow — RGB

Soft neon halo

text-shadow: 0 0 14px rgba(100, 91, 140, 0.45);
Div box shadow
Elevated card
box-shadow: 0 12px 32px -8px rgba(100, 91, 140, 0.45);
Border & gradient
Gradient panel
border: 3px solid #645b8c;
background: linear-gradient(135deg, #645b8c, #855B8C);
Gradient text

Gradient headline

background: linear-gradient(90deg, #645b8c, #8C5B87);
-webkit-background-clip: text;
color: transparent;
Focus ring
Focused control
outline: 2px solid #645b8c;
outline-offset: 3px;
Underline & caret

Marked up text

text-decoration-color: #645b8c;
caret-color: #645b8c;
Left rule
Pull quote or callout
border-left: 4px solid #645b8c;
Ring + tint
Selected chip
background: #F1F0F5;
box-shadow: inset 0 0 0 2px #645b8c;
Conic badge
68%
background: conic-gradient(#645b8c 68%, #e2e8f0 0);

Transparency

What each alpha value actually composites to. The top row is #645b8c 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(100, 91, 140, 0.5)
rgb(100 91 140 / 50%)
#645b8c80
hsl(251 21% 45% / 50%)
color-mix(in srgb, #645b8c 50%, transparent)
Alpha8-digit hexFlat on white
10%#645b8c1a#F0EFF4
20%#645b8c33#E0DEE8
40%#645b8c66#C1BDD1
60%#645b8c99#A29DBA
80%#645b8ccc#837CA3

Gradients from #645b8c

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, #837BA9, #645b8c 45%, #37324D);
Duotone
A short hue run reads richer than a flat fill
background: linear-gradient(120deg, #645b8c, #774F79);
Complement sweep
Loud — keep it behind large type only
background: linear-gradient(90deg, #645b8c, #838C5B);
Spotlight
Hero panels and app headers
background: radial-gradient(120% 120% at 20% 0%, #958EB5 0%, #645b8c 45%, #37324D 100%);
Soft wash
Section backgrounds that stay readable
background: linear-gradient(180deg, #F6F6F9, #ffffff);
Mesh
Ambient background, no image weight
background: radial-gradient(60% 60% at 15% 20%, #7588A5 0%, transparent 60%), radial-gradient(55% 55% at 85% 15%, #91689D 0%, transparent 60%), radial-gradient(70% 70% at 50% 95%, #37324D 0%, transparent 65%), #645b8c;

Monochromatic scale

Palettes built from #645b8c

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.

#645b8c 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 3.42:1 — lift it to #786FA1 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.

#645b8c, answered

What color is #645b8c?

#645b8c is a balanced soft blue, closest to Dark Slate Blue (ΔE2000 11.1). It sits at 251° on the hue wheel with 21% saturation and 45% lightness, which reads as cool.

What is the RGB value of #645b8c?

rgb(100, 91, 140) — 100 red, 91 green and 140 blue out of 255, or 39.2% / 35.7% / 54.9% by channel.

What is #645b8c in HSL and HSV?

hsl(251, 21%, 45%) and hsv(251, 35%, 55%). HSL is what CSS takes; HSV is what your design tool's picker shows, which is why the saturation numbers rarely match.

Is #645b8c a light or a dark color?

It is a dark color. Relative luminance is 0.1208 and perceived brightness is 39%, so white text on it reaches 6.15:1.

Should I use black or white text on #645b8c?

White. It scores 6.15:1 against #645b8c, versus 3.42:1 for black — AA at any size.

Is #645b8c accessible on a white background?

#645b8c on white scores 6.15:1, which clears AA at every size but not AAA.

What is the complementary color of #645b8c?

#838C5B sits directly opposite on the wheel. Softer options are the split-complements #8C7C5B and #6B8C5B, which give the same contrast with far less vibration.

What colors go well with #645b8c?

For interface work: #F6F6F9 as the surface, #D1CEDF for borders, #635A8B for secondary text, #918D56 as an accent and #37324D for hover and pressed states. For a palette, the analogous pair #5B6B8C and #7C5B8C stays calm, while #838C5B is the loudest partner.

What is #645b8c in CMYK for printing?

cmyk(29%, 35%, 0%, 45%). This is a screen-to-ink approximation — ask your printer for a proof before committing to a run.

Is #645b8c warm or cool?

Cool — it scores 66 on a scale where 0 is the warmest orange and 100 the coolest azure. Nudged warmer it becomes #765B8C; nudged cooler, #59638E.

Which Tailwind color is closest to #645b8c?

The slate family — its 500 step is #64748b, ΔE2000 13.1 away. That is a visible difference, so define #645b8c as a custom token rather than reaching for the built-in.

How do I use #645b8c in Tailwind CSS?

Inline it as an arbitrary value with bg-[#645b8c] or text-[#645b8c], 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 #645b8c with 50% opacity?

rgba(100, 91, 140, 0.5), or #645b8c80 in eight-digit hex. Over white that composites to #B2ADC6; over black, #322E46.

Is #645b8c a web-safe color?

No. The nearest web-safe colour is #666699, ΔE2000 4.5 away. The palette only matters for legacy displays and some email clients now.

What does the color #645b8c 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 moderate chroma the association is present but not shouted.

What gradient works with #645b8c?

The safest is same-hue elevation: linear-gradient(135deg, #837BA9, #645b8c 45%, #37324D). For more colour, a short hue run to #774F79 keeps it rich without turning muddy.

Work with #645b8c in the Color Lab

Every tool opens with this colour already loaded.

Every value on this page is computed from #645b8c at request time — conversions, contrast ratios and ΔE distances are calculated, never looked up.