#666DD1
Closest named color: Dark Periwinkle (#665FD1). oklch(57.8% 0.151 277.5), rgb(102, 109, 209).
Aa
Black text reads best on this color (4.67:1).
About this color
#666DD1 is a medium-dark, vivid blue. In OKLCH its lightness is 58%, its chroma 0.151 and its hue 278°. Its hue sits on the cool side of the wheel. The nearest named color is Dark Periwinkle (#665FD1), ΔE 0.035 away. Black text reads best on it, at 4.67:1.
| Hue family | Blues |
| Lightness | medium-dark (58%) |
| Chroma | vivid (0.151) |
| Temperature | cool |
| Nearest name | Dark Periwinkle (#665FD1) |
| Black text | 4.67:1 |
| White text | 4.49:1 |
Values
| HEX | #666DD1 |
| RGB | rgb(102, 109, 209) |
| HSL | hsl(236, 54%, 61%) |
| OKLCH | oklch(57.8% 0.151 277.5) |
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 #666DD1 | 4.49:1 | AA large text | Lc -76.5 | Fine for body text |
| Black text on #666DD1 | 4.67:1 | AA | Lc 33.1 | Non-text elements, placeholder text |
| #666DD1 text on white | 4.49:1 | AA large text | Lc 71.0 | Content text, not long reading |
| #666DD1 text on black | 4.67:1 | AA | Lc -30.7 | 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
#E6E9F7
oklch(93.6% 0.019 276.3)
-
Step 200
200
#D2D7F3
oklch(88.4% 0.039 277.6)
-
Step 300
300
#B5BDED
oklch(80.9% 0.068 277.4)
-
Step 400
400
#909AE4
oklch(70.8% 0.109 277.3)
-
Step 500
500
#767FDC
oklch(63.1% 0.139 277.5)
-
Step 600
600 (this color)
#666DD1
oklch(57.8% 0.151 277.5)
-
Step 700
700
#5054AE
oklch(49% 0.141 277.9)
-
Step 800
800
#41468D
oklch(42.8% 0.116 277.3)
-
Step 900
900
#373B71
oklch(37.7% 0.091 277.9)
-
Step 950
950
#202342
oklch(27% 0.057 277.6)
#666DD1 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) | #407BD5 | 0.051 |
| Deuteranopia (no green cones) | #3573CF | 0.053 |
| Tritanopia (no blue cones) | #398395 | 0.133 |
| Achromatopsia (no color) | #777777 | 0.152 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #666DD1
#666DD1
oklch(57.8% 0.151 277.5)
- #8D7900
#8D7900
oklch(57.7% 0.119 97.6)
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 #666DD1, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- Dark Periwinkle #665FD1 ΔE 0.035
- Light Indigo #6D5ACF ΔE 0.046
- Slate Blue #6A5ACD ΔE 0.046
- Royal Blue #4169E1 ΔE 0.053
- Iris #6258C4 ΔE 0.055
- Medium Slate Blue #7B68EE ΔE 0.055
- Cornflower #6A79F7 ΔE 0.062
- Windows Blue #3778BF ΔE 0.065
Use #666DD1 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.