#666F91
Closest named color: Metallic Blue (#4F738E). oklch(54.7% 0.054 273), rgb(102, 111, 145).
Aa
White text reads best on this color (4.94:1).
About this color
#666F91 is a medium-dark, muted blue. In OKLCH its lightness is 55%, its chroma 0.054 and its hue 273°. Its hue sits on the cool side of the wheel. The nearest named color is Metallic Blue (#4F738E), ΔE 0.032 away. White text reads best on it, at 4.94:1.
| Hue family | Blues |
| Lightness | medium-dark (55%) |
| Chroma | muted (0.054) |
| Temperature | cool |
| Nearest name | Metallic Blue (#4F738E) |
| Black text | 4.24:1 |
| White text | 4.94:1 |
Values
| HEX | #666F91 |
| RGB | rgb(102, 111, 145) |
| HSL | hsl(227, 17%, 48%) |
| OKLCH | oklch(54.7% 0.054 273) |
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 #666F91 | 4.94:1 | AA | Lc -79.6 | Fine for body text |
| Black text on #666F91 | 4.24:1 | AA large text | Lc 29.9 | Dividers and decoration only |
| #666F91 text on white | 4.94:1 | AA | Lc 74.2 | Content text, not long reading |
| #666F91 text on black | 4.24:1 | AA large text | Lc -27.5 | Dividers and decoration only |
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
#F5F5F8
oklch(97.1% 0.004 286.3)
-
Step 100
100
#E8EAEF
oklch(93.7% 0.007 268.5)
-
Step 200
200
#D6D9E2
oklch(88.6% 0.013 271.3)
-
Step 300
300
#BBC0D1
oklch(80.9% 0.024 272.8)
-
Step 400
400
#989FBA
oklch(70.6% 0.04 273.9)
-
Step 500
500
#7F88A8
oklch(63.1% 0.049 272.6)
-
Step 600
600 (this color)
#666F91
oklch(54.7% 0.054 273)
-
Step 700
700
#575F7E
oklch(49.1% 0.051 273.2)
-
Step 800
800
#474E66
oklch(42.7% 0.041 271.9)
-
Step 900
900
#3C4153
oklch(37.8% 0.032 272.7)
-
Step 950
950
#232631
oklch(27% 0.021 273)
#666F91 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) | #657293 | 0.008 |
| Deuteranopia (no green cones) | #626F90 | 0.006 |
| Tritanopia (no blue cones) | #5B757B | 0.047 |
| Achromatopsia (no color) | #707070 | 0.054 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #666F91
#666F91
oklch(54.7% 0.054 273)
- #7C704C
#7C704C
oklch(54.7% 0.054 91.8)
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 #666F91, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- Metallic Blue #4F738E ΔE 0.032
- Dull Blue #49759C ΔE 0.038
- Stormy Blue #507B9C ΔE 0.040
- Battleship Gray #6C757D ΔE 0.042
- Grey Purple #826D8C ΔE 0.042
- Grey Blue #647D8E ΔE 0.043
- Cerulean #457B9D ΔE 0.048
- Battleship Grey #6B7C85 ΔE 0.049
Use #666F91 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.