#666BCF
Closest named color: Dark Periwinkle (#665FD1). oklch(57.3% 0.151 278.3), rgb(102, 107, 207).
Aa
White text reads best on this color (4.59:1).
About this color
#666BCF is a medium-dark, vivid blue. In OKLCH its lightness is 57%, its chroma 0.151 and its hue 278°. Its hue sits on the cool side of the wheel. The nearest named color is Dark Periwinkle (#665FD1), ΔE 0.030 away. White text reads best on it, at 4.59:1.
| Hue family | Blues |
| Lightness | medium-dark (57%) |
| Chroma | vivid (0.151) |
| Temperature | cool |
| Nearest name | Dark Periwinkle (#665FD1) |
| Black text | 4.56:1 |
| White text | 4.59:1 |
Values
| HEX | #666BCF |
| RGB | rgb(102, 107, 207) |
| HSL | hsl(237, 52%, 61%) |
| OKLCH | oklch(57.3% 0.151 278.3) |
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 #666BCF | 4.59:1 | AA | Lc -77.2 | Fine for body text |
| Black text on #666BCF | 4.56:1 | AA | Lc 32.4 | Non-text elements, placeholder text |
| #666BCF text on white | 4.59:1 | AA | Lc 71.7 | Content text, not long reading |
| #666BCF text on black | 4.56:1 | 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
#F4F5FC
oklch(97.1% 0.009 279.7)
-
Step 100
100
#E6E9F7
oklch(93.6% 0.019 276.3)
-
Step 200
200
#D3D7F3
oklch(88.5% 0.039 279.1)
-
Step 300
300
#B6BDED
oklch(80.9% 0.068 278.3)
-
Step 400
400
#9199E4
oklch(70.6% 0.11 278.5)
-
Step 500
500
#777EDC
oklch(63% 0.14 278.3)
-
Step 600
600 (this color)
#666BCF
oklch(57.3% 0.151 278.3)
-
Step 700
700
#5154AE
oklch(49.1% 0.141 278.4)
-
Step 800
800
#42458D
oklch(42.6% 0.117 278.4)
-
Step 900
900
#373B71
oklch(37.7% 0.091 277.9)
-
Step 950
950
#202342
oklch(27% 0.057 277.6)
#666BCF 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) | #3D79D3 | 0.053 |
| Deuteranopia (no green cones) | #3371CD | 0.056 |
| Tritanopia (no blue cones) | #3B8193 | 0.133 |
| Achromatopsia (no color) | #757575 | 0.152 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #666BCF
#666BCF
oklch(57.3% 0.151 278.3)
- #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 #666BCF, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- Dark Periwinkle #665FD1 ΔE 0.030
- Slate Blue #6A5ACD ΔE 0.041
- Light Indigo #6D5ACF ΔE 0.041
- Iris #6258C4 ΔE 0.049
- Royal Blue #4169E1 ΔE 0.053
- Medium Slate Blue #7B68EE ΔE 0.057
- Windows Blue #3778BF ΔE 0.066
- Cornflower #6A79F7 ΔE 0.067
Use #666BCF 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.