#666BE4
Closest named color: Medium Slate Blue (#7B68EE). oklch(58.7% 0.18 277.5), rgb(102, 107, 228).
Aa
Black text reads best on this color (4.78:1).
About this color
#666BE4 is a medium-dark, vivid blue. In OKLCH its lightness is 59%, its chroma 0.180 and its hue 278°. Its hue sits on the cool side of the wheel. The nearest named color is Medium Slate Blue (#7B68EE), ΔE 0.034 away. Black text reads best on it, at 4.78:1.
| Hue family | Blues |
| Lightness | medium-dark (59%) |
| Chroma | vivid (0.180) |
| Temperature | cool |
| Nearest name | Medium Slate Blue (#7B68EE) |
| Black text | 4.78:1 |
| White text | 4.38:1 |
Values
| HEX | #666BE4 |
| RGB | rgb(102, 107, 228) |
| HSL | hsl(238, 70%, 65%) |
| OKLCH | oklch(58.7% 0.18 277.5) |
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 #666BE4 | 4.38:1 | AA large text | Lc -75.6 | Fine for body text |
| Black text on #666BE4 | 4.78:1 | AA | Lc 34.0 | Non-text elements, placeholder text |
| #666BE4 text on white | 4.38:1 | AA large text | Lc 70.1 | Content text, not long reading |
| #666BE4 text on black | 4.78:1 | AA | Lc -31.6 | 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
#F3F5FD
oklch(97.1% 0.011 274.9)
-
Step 100
100
#E6E9FA
oklch(93.7% 0.023 277.9)
-
Step 200
200
#D1D7F7
oklch(88.5% 0.044 277.1)
-
Step 300
300
#B3BCF5
oklch(80.8% 0.081 277.4)
-
Step 400
400
#8D98F0
oklch(70.7% 0.129 277.2)
-
Step 500
500
#737BEB
oklch(63% 0.166 277.4)
-
Step 600
600 (this color)
#666BE4
oklch(58.7% 0.18 277.5)
-
Step 700
700
#4E50BD
oklch(49.2% 0.167 277.5)
-
Step 800
800
#3F4299
oklch(42.7% 0.139 277.2)
-
Step 900
900
#353979
oklch(37.7% 0.107 277.3)
-
Step 950
950
#1F2247
oklch(27.1% 0.068 277.3)
#666BE4 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) | #227EE8 | 0.070 |
| Deuteranopia (no green cones) | #0073E1 | 0.074 |
| Tritanopia (no blue cones) | #23879D | 0.158 |
| Achromatopsia (no color) | #787878 | 0.181 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #666BE4
#666BE4
oklch(58.7% 0.18 277.5)
- #907C00
#907C00
oklch(58.7% 0.121 97.8)
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 #666BE4, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- Medium Slate Blue #7B68EE ΔE 0.034
- Dark Periwinkle #665FD1 ΔE 0.039
- Cornflower #6A79F7 ΔE 0.043
- Royal Blue #4169E1 ΔE 0.046
- Light Indigo #6D5ACF ΔE 0.049
- Slate Blue #6A5ACD ΔE 0.051
- Neon Blue #4361EE ΔE 0.055
- Purpley #8756E4 ΔE 0.064
Use #666BE4 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.