#666AD3
Closest named color: Dark Periwinkle (#665FD1). oklch(57.4% 0.158 278.5), rgb(102, 106, 211).
Aa
White text reads best on this color (4.59:1).
About this color
#666AD3 is a medium-dark, vivid blue. In OKLCH its lightness is 57%, its chroma 0.158 and its hue 279°. Its hue sits on the cool side of the wheel. The nearest named color is Dark Periwinkle (#665FD1), ΔE 0.027 away. White text reads best on it, at 4.59:1.
| Hue family | Blues |
| Lightness | medium-dark (57%) |
| Chroma | vivid (0.158) |
| Temperature | cool |
| Nearest name | Dark Periwinkle (#665FD1) |
| Black text | 4.56:1 |
| White text | 4.59:1 |
Values
| HEX | #666AD3 |
| RGB | rgb(102, 106, 211) |
| HSL | hsl(238, 55%, 61%) |
| OKLCH | oklch(57.4% 0.158 278.5) |
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 #666AD3 | 4.59:1 | AA | Lc -77.2 | Fine for body text |
| Black text on #666AD3 | 4.56:1 | AA | Lc 32.4 | Non-text elements, placeholder text |
| #666AD3 text on white | 4.59:1 | AA | Lc 71.7 | Content text, not long reading |
| #666AD3 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
#E6E9F8
oklch(93.6% 0.02 276.9)
-
Step 200
200
#D3D7F4
oklch(88.5% 0.04 279.3)
-
Step 300
300
#B6BDEF
oklch(81% 0.071 278.5)
-
Step 400
400
#9199E7
oklch(70.8% 0.114 278.6)
-
Step 500
500
#777EDF
oklch(63.2% 0.144 278.3)
-
Step 600
600 (this color)
#666AD3
oklch(57.4% 0.158 278.5)
-
Step 700
700
#5153B1
oklch(49.1% 0.146 278.6)
-
Step 800
800
#424490
oklch(42.7% 0.123 278.7)
-
Step 900
900
#373A73
oklch(37.6% 0.096 278.5)
-
Step 950
950
#202343
oklch(27.1% 0.059 277.6)
#666AD3 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) | #377AD7 | 0.059 |
| Deuteranopia (no green cones) | #2B71D1 | 0.061 |
| Tritanopia (no blue cones) | #388194 | 0.138 |
| Achromatopsia (no color) | #757575 | 0.159 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #666AD3
#666AD3
oklch(57.4% 0.158 278.5)
- #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 #666AD3, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- Dark Periwinkle #665FD1 ΔE 0.027
- Light Indigo #6D5ACF ΔE 0.038
- Slate Blue #6A5ACD ΔE 0.038
- Iris #6258C4 ΔE 0.049
- Royal Blue #4169E1 ΔE 0.049
- Medium Slate Blue #7B68EE ΔE 0.052
- Cornflower #6A79F7 ΔE 0.063
- Warm Blue #4B57DB ΔE 0.064
Use #666AD3 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.