#666BD3
Closest named color: Dark Periwinkle (#665FD1). oklch(57.5% 0.157 278.2), rgb(102, 107, 211).
Aa
Black text reads best on this color (4.60:1).
About this color
#666BD3 is a medium-dark, vivid blue. In OKLCH its lightness is 58%, its chroma 0.157 and its hue 278°. Its hue sits on the cool side of the wheel. The nearest named color is Dark Periwinkle (#665FD1), ΔE 0.029 away. Black text reads best on it, at 4.60:1.
| Hue family | Blues |
| Lightness | medium-dark (58%) |
| Chroma | vivid (0.157) |
| Temperature | cool |
| Nearest name | Dark Periwinkle (#665FD1) |
| Black text | 4.60:1 |
| White text | 4.55:1 |
Values
| HEX | #666BD3 |
| RGB | rgb(102, 107, 211) |
| HSL | hsl(237, 55%, 61%) |
| OKLCH | oklch(57.5% 0.157 278.2) |
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 #666BD3 | 4.55:1 | AA | Lc -76.9 | Fine for body text |
| Black text on #666BD3 | 4.60:1 | AA | Lc 32.7 | Non-text elements, placeholder text |
| #666BD3 text on white | 4.55:1 | AA | Lc 71.4 | Content text, not long reading |
| #666BD3 text on black | 4.60:1 | AA | Lc -30.3 | 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
#F4F5FC
oklch(97.1% 0.009 279.7)
-
Step 100
100
#E6E9F8
oklch(93.6% 0.02 276.9)
-
Step 200
200
#D3D7F4
oklch(88.5% 0.04 279.3)
-
Step 300
300
#B5BDEE
oklch(80.9% 0.07 277.5)
-
Step 400
400
#9099E6
oklch(70.7% 0.113 278)
-
Step 500
500
#777EDF
oklch(63.2% 0.144 278.3)
-
Step 600
600 (this color)
#666BD3
oklch(57.5% 0.157 278.2)
-
Step 700
700
#5053B1
oklch(49% 0.146 278.2)
-
Step 800
800
#42458F
oklch(42.8% 0.12 278.3)
-
Step 900
900
#373A72
oklch(37.6% 0.094 278.5)
-
Step 950
950
#202343
oklch(27.1% 0.059 277.6)
#666BD3 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) | #397AD7 | 0.056 |
| Deuteranopia (no green cones) | #2E72D1 | 0.059 |
| Tritanopia (no blue cones) | #388295 | 0.137 |
| Achromatopsia (no color) | #767676 | 0.157 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #666BD3
#666BD3
oklch(57.5% 0.157 278.2)
- #8C7900
#8C7900
oklch(57.6% 0.119 98.2)
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 #666BD3, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- Dark Periwinkle #665FD1 ΔE 0.029
- Light Indigo #6D5ACF ΔE 0.041
- Slate Blue #6A5ACD ΔE 0.041
- Royal Blue #4169E1 ΔE 0.050
- Iris #6258C4 ΔE 0.051
- Medium Slate Blue #7B68EE ΔE 0.052
- Cornflower #6A79F7 ΔE 0.062
- Warm Blue #4B57DB ΔE 0.066
Use #666BD3 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.