#666BC5
Closest named color: Dark Periwinkle (#665FD1). oklch(56.7% 0.137 278.7), rgb(102, 107, 197).
Aa
White text reads best on this color (4.69:1).
About this color
#666BC5 is a medium-dark, moderately saturated blue. In OKLCH its lightness is 57%, its chroma 0.137 and its hue 279°. Its hue sits on the cool side of the wheel. The nearest named color is Dark Periwinkle (#665FD1), ΔE 0.037 away. White text reads best on it, at 4.69:1.
| Hue family | Blues |
| Lightness | medium-dark (57%) |
| Chroma | moderately saturated (0.137) |
| Temperature | cool |
| Nearest name | Dark Periwinkle (#665FD1) |
| Black text | 4.47:1 |
| White text | 4.69:1 |
Values
| HEX | #666BC5 |
| RGB | rgb(102, 107, 197) |
| HSL | hsl(237, 45%, 59%) |
| OKLCH | oklch(56.7% 0.137 278.7) |
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 #666BC5 | 4.69:1 | AA | Lc -77.9 | Fine for body text |
| Black text on #666BC5 | 4.47:1 | AA large text | Lc 31.6 | Non-text elements, placeholder text |
| #666BC5 text on white | 4.69:1 | AA | Lc 72.4 | Content text, not long reading |
| #666BC5 text on black | 4.47:1 | AA large text | Lc -29.3 | 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
#E7E9F6
oklch(93.6% 0.018 279.1)
-
Step 200
200
#D4D7F0
oklch(88.5% 0.034 280.2)
-
Step 300
300
#B7BDE9
oklch(80.8% 0.062 278.8)
-
Step 400
400
#939ADE
oklch(70.7% 0.1 279)
-
Step 500
500
#7980D4
oklch(63.1% 0.126 278.5)
-
Step 600
600 (this color)
#666BC5
oklch(56.7% 0.137 278.7)
-
Step 700
700
#5256A7
oklch(49.1% 0.127 278.5)
-
Step 800
800
#434787
oklch(42.7% 0.105 278.3)
-
Step 900
900
#383C6C
oklch(37.7% 0.082 278.1)
-
Step 950
950
#21233F
oklch(26.9% 0.052 279.2)
#666BC5 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) | #4678C8 | 0.047 |
| Deuteranopia (no green cones) | #3E70C3 | 0.047 |
| Tritanopia (no blue cones) | #437E8E | 0.120 |
| Achromatopsia (no color) | #747474 | 0.137 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #666BC5
#666BC5
oklch(56.7% 0.137 278.7)
- #887600
#887600
oklch(56.5% 0.117 98.6)
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 #666BC5, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- Dark Periwinkle #665FD1 ΔE 0.037
- Slate Blue #6A5ACD ΔE 0.045
- Light Indigo #6D5ACF ΔE 0.046
- Iris #6258C4 ΔE 0.049
- French Blue #436BAD ΔE 0.059
- Windows Blue #3778BF ΔE 0.060
- Royal Blue #4169E1 ΔE 0.062
- Deep Lavender #8D5EB7 ΔE 0.068
Use #666BC5 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.