#666FBB
Closest named color: French Blue (#436BAD). oklch(56.9% 0.117 276.9), rgb(102, 111, 187).
Aa
White text reads best on this color (4.60:1).
About this color
#666FBB is a medium-dark, moderately saturated blue. In OKLCH its lightness is 57%, its chroma 0.117 and its hue 277°. Its hue sits on the cool side of the wheel. The nearest named color is French Blue (#436BAD), ΔE 0.052 away. White text reads best on it, at 4.60:1.
| Hue family | Blues |
| Lightness | medium-dark (57%) |
| Chroma | moderately saturated (0.117) |
| Temperature | cool |
| Nearest name | French Blue (#436BAD) |
| Black text | 4.55:1 |
| White text | 4.60:1 |
Values
| HEX | #666FBB |
| RGB | rgb(102, 111, 187) |
| HSL | hsl(234, 38%, 57%) |
| OKLCH | oklch(56.9% 0.117 276.9) |
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 #666FBB | 4.60:1 | AA | Lc -77.4 | Fine for body text |
| Black text on #666FBB | 4.55:1 | AA | Lc 32.2 | Non-text elements, placeholder text |
| #666FBB text on white | 4.60:1 | AA | Lc 71.9 | Content text, not long reading |
| #666FBB text on black | 4.55:1 | AA | Lc -29.8 | 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
#F4F5FA
oklch(97.1% 0.007 277.2)
-
Step 100
100
#E7E9F4
oklch(93.6% 0.015 277.8)
-
Step 200
200
#D4D8ED
oklch(88.6% 0.029 277.2)
-
Step 300
300
#B7BEE3
oklch(80.8% 0.053 276.7)
-
Step 400
400
#939CD5
oklch(70.7% 0.084 277.1)
-
Step 500
500
#7983CA
oklch(63.2% 0.107 276.8)
-
Step 600
600 (this color)
#666FBB
oklch(56.9% 0.117 276.9)
-
Step 700
700
#52599D
oklch(49.1% 0.108 277.2)
-
Step 800
800
#434980
oklch(42.7% 0.091 277.1)
-
Step 900
900
#383D66
oklch(37.5% 0.07 277.2)
-
Step 950
950
#21243C
oklch(27% 0.045 277.5)
#666FBB 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) | #5378BE | 0.031 |
| Deuteranopia (no green cones) | #4C72B9 | 0.033 |
| Tritanopia (no blue cones) | #497F8C | 0.104 |
| Achromatopsia (no color) | #757575 | 0.117 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #666FBB
#666FBB
oklch(56.9% 0.117 276.9)
- #8B7600
#8B7600
oklch(56.9% 0.117 96.6)
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 #666FBB, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- French Blue #436BAD ΔE 0.052
- Windows Blue #3778BF ΔE 0.053
- Dark Periwinkle #665FD1 ΔE 0.057
- Flat Blue #3C73A8 ΔE 0.060
- Slate Blue #6A5ACD ΔE 0.063
- Steel Blue #4682B4 ΔE 0.064
- Iris #6258C4 ΔE 0.064
- Cool Blue #4984B8 ΔE 0.064
Use #666FBB 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.