#666FDD
Closest named color: Dark Periwinkle (#665FD1). oklch(59% 0.165 276.6), rgb(102, 111, 221).
Aa
Black text reads best on this color (4.88:1).
About this color
#666FDD is a medium-dark, vivid blue. In OKLCH its lightness is 59%, its chroma 0.165 and its hue 277°. Its hue sits on the cool side of the wheel. The nearest named color is Dark Periwinkle (#665FD1), ΔE 0.041 away. Black text reads best on it, at 4.88:1.
| Hue family | Blues |
| Lightness | medium-dark (59%) |
| Chroma | vivid (0.165) |
| Temperature | cool |
| Nearest name | Dark Periwinkle (#665FD1) |
| Black text | 4.88:1 |
| White text | 4.30:1 |
Values
| HEX | #666FDD |
| RGB | rgb(102, 111, 221) |
| HSL | hsl(235, 64%, 63%) |
| OKLCH | oklch(59% 0.165 276.6) |
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 #666FDD | 4.30:1 | AA large text | Lc -75.0 | Fine for body text |
| Black text on #666FDD | 4.88:1 | AA | Lc 34.6 | Non-text elements, placeholder text |
| #666FDD text on white | 4.30:1 | AA large text | Lc 69.5 | Content text, not long reading |
| #666FDD text on black | 4.88:1 | AA | Lc -32.2 | 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
#F3F5FC
oklch(97.1% 0.01 273.4)
-
Step 100
100
#E6E9F9
oklch(93.6% 0.022 277.5)
-
Step 200
200
#D1D7F5
oklch(88.4% 0.042 276.6)
-
Step 300
300
#B3BDF1
oklch(80.9% 0.074 276.1)
-
Step 400
400
#8D99EA
oklch(70.6% 0.119 276.5)
-
Step 500
500
#737EE4
oklch(63.2% 0.152 276.5)
-
Step 600
600 (this color)
#666FDD
oklch(59% 0.165 276.6)
-
Step 700
700
#4D53B6
oklch(49.2% 0.154 276.5)
-
Step 800
800
#3F4493
oklch(42.7% 0.128 276.8)
-
Step 900
900
#353A75
oklch(37.6% 0.1 276.8)
-
Step 950
950
#1F2345
oklch(27.1% 0.063 276.3)
#666FDD 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) | #387FE1 | 0.057 |
| Deuteranopia (no green cones) | #2875DB | 0.060 |
| Tritanopia (no blue cones) | #2C889C | 0.145 |
| Achromatopsia (no color) | #7A7A7A | 0.166 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #666FDD
#666FDD
oklch(59% 0.165 276.6)
- #927C00
#927C00
oklch(58.9% 0.121 96.6)
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 #666FDD, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- Dark Periwinkle #665FD1 ΔE 0.041
- Medium Slate Blue #7B68EE ΔE 0.043
- Cornflower #6A79F7 ΔE 0.045
- Royal Blue #4169E1 ΔE 0.049
- Light Indigo #6D5ACF ΔE 0.052
- Slate Blue #6A5ACD ΔE 0.053
- Soft Blue #6488EA ΔE 0.064
- Neon Blue #4361EE ΔE 0.064
Use #666FDD 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.