#666CCB
Closest named color: Dark Periwinkle (#665FD1). oklch(57.2% 0.144 278.1), rgb(102, 108, 203).
Aa
White text reads best on this color (4.59:1).
About this color
#666CCB is a medium-dark, vivid blue. In OKLCH its lightness is 57%, its chroma 0.144 and its hue 278°. Its hue sits on the cool side of the wheel. The nearest named color is Dark Periwinkle (#665FD1), ΔE 0.035 away. White text reads best on it, at 4.59:1.
| Hue family | Blues |
| Lightness | medium-dark (57%) |
| Chroma | vivid (0.144) |
| Temperature | cool |
| Nearest name | Dark Periwinkle (#665FD1) |
| Black text | 4.57:1 |
| White text | 4.59:1 |
Values
| HEX | #666CCB |
| RGB | rgb(102, 108, 203) |
| HSL | hsl(236, 49%, 60%) |
| OKLCH | oklch(57.2% 0.144 278.1) |
Contrast
WCAG 2 contrast ratios are the conformance target: AA needs 4.5:1 for body text and 3:1 for large text, AAA needs 7:1. APCA Lc values are supplementary guidance from the WCAG 3 drafts.
| Pair | WCAG 2 | Result | APCA | APCA guidance |
|---|---|---|---|---|
| White text on #666CCB | 4.59:1 | AA | Lc -77.2 | Fine for body text |
| Black text on #666CCB | 4.57:1 | AA | Lc 32.4 | Non-text elements, placeholder text |
| #666CCB text on white | 4.59:1 | AA | Lc 71.7 | Content text, not long reading |
| #666CCB text on black | 4.57:1 | AA | Lc -30.0 | Dividers and decoration only |
Tints and shades
A 50–950 scale built in OKLCH: the hue is held, lightness follows a Tailwind v4-like curve, and every step is kept inside the sRGB gamut. This color sits at step 600.
-
Step 50
50
#F4F5FB
oklch(97.1% 0.008 278.6)
-
Step 100
100
#E7E9F7
oklch(93.7% 0.019 279.5)
-
Step 200
200
#D3D7F1
oklch(88.4% 0.036 278.7)
-
Step 300
300
#B6BDEB
oklch(80.9% 0.065 278.1)
-
Step 400
400
#919AE1
oklch(70.7% 0.104 277.8)
-
Step 500
500
#787FD8
oklch(63% 0.133 278.4)
-
Step 600
600 (this color)
#666CCB
oklch(57.2% 0.144 278.1)
-
Step 700
700
#5155AB
oklch(49.1% 0.135 278.2)
-
Step 800
800
#42468A
oklch(42.6% 0.111 278.1)
-
Step 900
900
#383B6F
oklch(37.7% 0.088 278.8)
-
Step 950
950
#202341
oklch(27% 0.056 277.7)
#666CCB with color blindness
Simulated with the Machado et al. (2009) model. ΔE is how far the color moves: below about 0.02 you would not notice a change.
| Vision | Seen as | Shift (ΔE) |
|---|---|---|
| Protanopia (no red cones) | #4379CE | 0.048 |
| Deuteranopia (no green cones) | #3A71C9 | 0.050 |
| Tritanopia (no blue cones) | #3E8092 | 0.125 |
| Achromatopsia (no color) | #757575 | 0.145 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #666CCB
#666CCB
oklch(57.2% 0.144 278.1)
- #8B7800
#8B7800
oklch(57.3% 0.118 98.1)
Analogous
Neighbouring hues, 30° either side.
Split complementary
The two hues beside the complement (150° and 210°).
Triadic
Three hues spaced 120° apart.
Palettes with this color
Curated palettes that contain a color within ΔE 0.04 (OKLab) of #666CCB, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- Dark Periwinkle #665FD1 ΔE 0.035
- Slate Blue #6A5ACD ΔE 0.044
- Light Indigo #6D5ACF ΔE 0.045
- Iris #6258C4 ΔE 0.051
- Royal Blue #4169E1 ΔE 0.057
- Windows Blue #3778BF ΔE 0.062
- Medium Slate Blue #7B68EE ΔE 0.063
- French Blue #436BAD ΔE 0.066
Use #666CCB in your product
Turn it into light and dark UI roles checked for contrast, then export to Tailwind v4, shadcn/ui, CSS or design tokens.