#666FCA
Closest named color: Dark Periwinkle (#665FD1). oklch(57.8% 0.139 276.9), rgb(102, 111, 202).
Aa
Black text reads best on this color (4.69:1).
About this color
#666FCA is a medium-dark, moderately saturated blue. In OKLCH its lightness is 58%, its chroma 0.139 and its hue 277°. Its hue sits on the cool side of the wheel. The nearest named color is Dark Periwinkle (#665FD1), ΔE 0.043 away. Black text reads best on it, at 4.69:1.
| Hue family | Blues |
| Lightness | medium-dark (58%) |
| Chroma | moderately saturated (0.139) |
| Temperature | cool |
| Nearest name | Dark Periwinkle (#665FD1) |
| Black text | 4.69:1 |
| White text | 4.47:1 |
Values
| HEX | #666FCA |
| RGB | rgb(102, 111, 202) |
| HSL | hsl(235, 49%, 60%) |
| OKLCH | oklch(57.8% 0.139 276.9) |
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 #666FCA | 4.47:1 | AA large text | Lc -76.4 | Fine for body text |
| Black text on #666FCA | 4.69:1 | AA | Lc 33.2 | Non-text elements, placeholder text |
| #666FCA text on white | 4.47:1 | AA large text | Lc 70.9 | Content text, not long reading |
| #666FCA text on black | 4.69:1 | AA | Lc -30.8 | 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
#F4F5FB
oklch(97.1% 0.008 278.6)
-
Step 100
100
#E6E9F6
oklch(93.6% 0.018 275.6)
-
Step 200
200
#D3D8F1
oklch(88.6% 0.035 276.7)
-
Step 300
300
#B6BEE9
oklch(81% 0.061 276.7)
-
Step 400
400
#909BDF
oklch(70.7% 0.1 276.5)
-
Step 500
500
#7681D6
oklch(63.2% 0.128 276.5)
-
Step 600
600 (this color)
#666FCA
oklch(57.8% 0.139 276.9)
-
Step 700
700
#5057A8
oklch(49.2% 0.128 276.9)
-
Step 800
800
#414788
oklch(42.6% 0.107 276.9)
-
Step 900
900
#373C6D
oklch(37.7% 0.083 277.2)
-
Step 950
950
#202440
oklch(27.1% 0.052 276.2)
#666FCA 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) | #497BCD | 0.042 |
| Deuteranopia (no green cones) | #4073C8 | 0.044 |
| Tritanopia (no blue cones) | #3F8293 | 0.121 |
| Achromatopsia (no color) | #777777 | 0.139 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #666FCA
#666FCA
oklch(57.8% 0.139 276.9)
- #8E7900
#8E7900
oklch(57.8% 0.119 96.9)
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 #666FCA, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- Dark Periwinkle #665FD1 ΔE 0.043
- Slate Blue #6A5ACD ΔE 0.052
- Light Indigo #6D5ACF ΔE 0.053
- Windows Blue #3778BF ΔE 0.058
- Iris #6258C4 ΔE 0.059
- Royal Blue #4169E1 ΔE 0.060
- French Blue #436BAD ΔE 0.065
- Medium Slate Blue #7B68EE ΔE 0.066
Use #666FCA 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.