#666FCC
Closest named color: Dark Periwinkle (#665FD1). oklch(57.9% 0.142 276.9), rgb(102, 111, 204).
Aa
Black text reads best on this color (4.71:1).
About this color
#666FCC is a medium-dark, vivid blue. In OKLCH its lightness is 58%, its chroma 0.142 and its hue 277°. Its hue sits on the cool side of the wheel. The nearest named color is Dark Periwinkle (#665FD1), ΔE 0.042 away. Black text reads best on it, at 4.71:1.
| Hue family | Blues |
| Lightness | medium-dark (58%) |
| Chroma | vivid (0.142) |
| Temperature | cool |
| Nearest name | Dark Periwinkle (#665FD1) |
| Black text | 4.71:1 |
| White text | 4.45:1 |
Values
| HEX | #666FCC |
| RGB | rgb(102, 111, 204) |
| HSL | hsl(235, 50%, 60%) |
| OKLCH | oklch(57.9% 0.142 276.9) |
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 #666FCC | 4.45:1 | AA large text | Lc -76.2 | Fine for body text |
| Black text on #666FCC | 4.71:1 | AA | Lc 33.3 | Non-text elements, placeholder text |
| #666FCC text on white | 4.45:1 | AA large text | Lc 70.8 | Content text, not long reading |
| #666FCC text on black | 4.71:1 | AA | Lc -30.9 | Non-text elements, placeholder text |
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
#E6E9F7
oklch(93.6% 0.019 276.3)
-
Step 200
200
#D3D8F1
oklch(88.6% 0.035 276.7)
-
Step 300
300
#B5BEEA
oklch(80.9% 0.063 275.9)
-
Step 400
400
#909BE0
oklch(70.8% 0.102 276.5)
-
Step 500
500
#7680D7
oklch(63% 0.131 277)
-
Step 600
600 (this color)
#666FCC
oklch(57.9% 0.142 276.9)
-
Step 700
700
#4F56AA
oklch(49.1% 0.132 276.8)
-
Step 800
800
#414789
oklch(42.7% 0.108 276.9)
-
Step 900
900
#373C6E
oklch(37.7% 0.085 277.2)
-
Step 950
950
#202340
oklch(26.9% 0.054 277.6)
#666FCC 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) | #477CCF | 0.045 |
| Deuteranopia (no green cones) | #3E73CA | 0.046 |
| Tritanopia (no blue cones) | #3D8394 | 0.124 |
| Achromatopsia (no color) | #777777 | 0.142 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #666FCC
#666FCC
oklch(57.9% 0.142 276.9)
- #8E7900
#8E7900
oklch(57.8% 0.119 96.9)
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 #666FCC, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- Dark Periwinkle #665FD1 ΔE 0.042
- Slate Blue #6A5ACD ΔE 0.052
- Light Indigo #6D5ACF ΔE 0.052
- Royal Blue #4169E1 ΔE 0.058
- Iris #6258C4 ΔE 0.059
- Windows Blue #3778BF ΔE 0.059
- Medium Slate Blue #7B68EE ΔE 0.063
- Cornflower #6A79F7 ΔE 0.067
Use #666FCC 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.