#666DDF
Closest named color: Dark Periwinkle (#665FD1). oklch(58.7% 0.171 277.1), rgb(102, 109, 223).
Aa
Black text reads best on this color (4.81:1).
About this color
#666DDF is a medium-dark, vivid blue. In OKLCH its lightness is 59%, its chroma 0.171 and its hue 277°. Its hue sits on the cool side of the wheel. The nearest named color is Dark Periwinkle (#665FD1), ΔE 0.038 away. Black text reads best on it, at 4.81:1.
| Hue family | Blues |
| Lightness | medium-dark (59%) |
| Chroma | vivid (0.171) |
| Temperature | cool |
| Nearest name | Dark Periwinkle (#665FD1) |
| Black text | 4.81:1 |
| White text | 4.35:1 |
Values
| HEX | #666DDF |
| RGB | rgb(102, 109, 223) |
| HSL | hsl(237, 65%, 64%) |
| OKLCH | oklch(58.7% 0.171 277.1) |
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 #666DDF | 4.35:1 | AA large text | Lc -75.4 | Fine for body text |
| Black text on #666DDF | 4.81:1 | AA | Lc 34.2 | Non-text elements, placeholder text |
| #666DDF text on white | 4.35:1 | AA large text | Lc 69.9 | Content text, not long reading |
| #666DDF text on black | 4.81:1 | AA | Lc -31.7 | 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
#F3F5FD
oklch(97.1% 0.011 274.9)
-
Step 100
100
#E6E9F9
oklch(93.6% 0.022 277.5)
-
Step 200
200
#D1D7F6
oklch(88.4% 0.043 276.8)
-
Step 300
300
#B4BDF3
oklch(81% 0.077 277.2)
-
Step 400
400
#8E99EC
oklch(70.8% 0.122 277.1)
-
Step 500
500
#737DE6
oklch(63.1% 0.156 276.8)
-
Step 600
600 (this color)
#666DDF
oklch(58.7% 0.171 277.1)
-
Step 700
700
#4E52B8
oklch(49.2% 0.158 277.2)
-
Step 800
800
#3F4395
oklch(42.6% 0.132 277.1)
-
Step 900
900
#353A77
oklch(37.8% 0.103 276.8)
-
Step 950
950
#1F2245
oklch(26.9% 0.064 277.4)
#666DDF 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) | #307EE3 | 0.062 |
| Deuteranopia (no green cones) | #1D74DD | 0.066 |
| Tritanopia (no blue cones) | #2A879C | 0.150 |
| Achromatopsia (no color) | #797979 | 0.171 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #666DDF
#666DDF
oklch(58.7% 0.171 277.1)
- #917C00
#917C00
oklch(58.8% 0.121 97.2)
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 #666DDF, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- Dark Periwinkle #665FD1 ΔE 0.038
- Medium Slate Blue #7B68EE ΔE 0.039
- Cornflower #6A79F7 ΔE 0.045
- Royal Blue #4169E1 ΔE 0.047
- Light Indigo #6D5ACF ΔE 0.049
- Slate Blue #6A5ACD ΔE 0.050
- Neon Blue #4361EE ΔE 0.060
- Iris #6258C4 ΔE 0.063
Use #666DDF 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.