#21f3cf
a balanced, electric cyan · cool · closest name: Aqua Marine
At a glance
Every number on this page in one read: what #21f3cf is made of, how bright it looks, and which way it leans.
Reads cool. Warm and cool siblings keep the same lightness, so you can swap one in without redoing your contrast maths.
Every format
| HEX | #21f3cf |
| RGB | rgb(33, 243, 207) |
| HSL | hsl(170, 90%, 54%) |
| CMYK | cmyk(86%, 0%, 15%, 5%) |
| LAB | lab(86.5 -55.1 4.0) |
| LCH | lch(86.5 55.2 175.8) |
| OKLCH | oklch(0.864 0.157 176.4) |
| Decimal | 2225103 |
| Display P3 | color(display-p3 0.129 0.953 0.812) |
Copy-ready code
/* CSS */
color: #21f3cf;
background-color: #21f3cf;
/* Tailwind (arbitrary) */
class="text-[#21f3cf] bg-[#21f3cf]"
/* SCSS */
$brand: #21f3cf;
/* SwiftUI */
Color(red: 0.129, green: 0.953, blue: 0.812)
/* Android */
Color.parseColor("#21f3cf")
/* Flutter */
Color(0xFF21F3CF)
/* Python / OpenCV (BGR) */
(207, 243, 33)Best text color
Only one of black and white can be right. This is the one, with the number that proves it.
Accessibility — WCAG contrast
Color scale — 50 to 950
A Tailwind-shaped ramp built around this exact hex. #21f3cf is pinned to step 500; the rest hold its hue and let saturation ease off at the extremes so the pale end never turns neon.
:root {
--brand-50: #F2FDFB;
--brand-100: #E5FBF7;
--brand-200: #C3F8EF;
--brand-300: #95F9E8;
--brand-400: #5FF6DC;
--brand-500: #21f3cf;
--brand-600: #0DE8C2;
--brand-700: #0BC1A2;
--brand-800: #089B82;
--brand-900: #0B705E;
--brand-950: #07463B;
--brand: #21f3cf;
--brand-ink: #000000;
}Colors that work with #21f3cf
Not a palette — a role sheet. Each swatch answers one question you will hit while building the component.
Surface, border, heading and body all derive from this one hue, so the screen stays coherent without a second palette.
Lightness flips, hue holds. The accent stays the anchor in both themes.
How to use #21f3cf
Derived from its contrast, chroma and lightness — not from taste.
- ✓Text and icons on dark surfaces
- ✓Primary buttons and calls to action
- ✓Focus rings, active and selected states
- ✓Brand accents, badges and data highlights
- ⚠Text of any size on white — fails WCAG AA
- ⚠Full-page backgrounds — tiring over long sessions
- ⚠Thin strokes and 1px borders — they disappear on light UI
- ⚠Pairing with a same-lightness hue — edges vibrate
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 | #F32145 | Directly opposite — maximum tension | |
| Analogous left | #21F366 | Neighbour, quieter | |
| Analogous right | #21AEF3 | Neighbour, quieter | |
| Split-complement 1 | #F321AE | Contrast without the clash | |
| Split-complement 2 | #F36621 | Contrast without the clash | |
| Triadic 1 | #CF21F3 | Even thirds — balanced and loud | |
| Triadic 2 | #F3CF21 | Even thirds — balanced and loud | |
| Tetradic | #6621F3 | Fourth corner of the square scheme |
RGB percentages
CMYK percentages
Color previews
#21f3cf text on a black background
contrast 14.79:1
#21f3cf text on a white background
contrast 1.42:1
CSS3 live lab
The quick brown fox
color: #21f3cf;
background-color: #21f3cf;
Glowing headline
text-shadow: 2px 2px 8px #21f3cf;
Soft neon halo
text-shadow: 0 0 14px rgba(33, 243, 207, 0.45);
box-shadow: 0 12px 32px -8px rgba(33, 243, 207, 0.45);
border: 3px solid #21f3cf; background: linear-gradient(135deg, #21f3cf, #218BF3);
Monochromatic scale
Palettes built from #21f3cf
Shades — darker
Tints — lighter
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.
Closest color with a full write-up: Aquamarine (#7fffd4) — ΔE2000 5.8 away, with its history, psychology and brand usage.
#21f3cf in the real world
Where a color in this family tends to land, and the interface roles it is usually asked to play.
Sits outside most CMYK gamuts — expect a duller press result, or specify a spot ink.
#21f3cf, answered
What color is #21f3cf?
#21f3cf is a balanced electric cyan, closest to Aqua Marine (ΔE2000 5.8). It sits at 170° on the hue wheel with 90% saturation and 54% lightness, which reads as cool.
What is the RGB value of #21f3cf?
rgb(33, 243, 207) — 33 red, 243 green and 207 blue out of 255, or 12.9% / 95.3% / 81.2% by channel.
Is #21f3cf a light or a dark color?
It is a light color. Relative luminance is 0.6893 and perceived brightness is 78%, so black text on it reaches 14.79:1.
Should I use black or white text on #21f3cf?
Black. It scores 14.79:1 against #21f3cf, versus 1.42:1 for white — AAA at any size.
What is the complementary color of #21f3cf?
#F32145 sits directly opposite on the wheel. Softer options are the split-complements #F321AE and #F36621, which give the same contrast with far less vibration.
What colors go well with #21f3cf?
For interface work: #F4FAF9 as the surface, #C0EDE5 for borders, #4B9B8D for secondary text, #F81C79 as an accent and #077965 for hover and pressed states. For a palette, the analogous pair #21F366 and #21AEF3 stays calm, while #F32145 is the loudest partner.
What is #21f3cf in CMYK for printing?
cmyk(86%, 0%, 15%, 5%). This is a screen-to-ink approximation — a color this saturated sits outside most CMYK gamuts and will print duller than it looks here.
Is #21f3cf warm or cool?
Cool — it scores 83 on a scale where 0 is the warmest orange and 100 the coolest azure. Nudged warmer it becomes #21F382; nudged cooler, #1FCFF5.