#637D91
Closest named color: Grey Blue (#647D8E). oklch(57.7% 0.043 241.6), rgb(99, 125, 145).
Aa
Black text reads best on this color (4.87:1).
About this color
#637D91 is a medium-dark, muted blue. In OKLCH its lightness is 58%, its chroma 0.043 and its hue 242°. Its hue sits on the cool side of the wheel. The nearest named color is Grey Blue (#647D8E), ΔE 0.005 away. Black text reads best on it, at 4.87:1.
| Hue family | Blues |
| Lightness | medium-dark (58%) |
| Chroma | muted (0.043) |
| Temperature | cool |
| Nearest name | Grey Blue (#647D8E) |
| Black text | 4.87:1 |
| White text | 4.30:1 |
Values
| HEX | #637D91 |
| RGB | rgb(99, 125, 145) |
| HSL | hsl(206, 19%, 48%) |
| OKLCH | oklch(57.7% 0.043 241.6) |
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 #637D91 | 4.30:1 | AA large text | Lc -75.3 | Fine for body text |
| Black text on #637D91 | 4.87:1 | AA | Lc 34.3 | Non-text elements, placeholder text |
| #637D91 text on white | 4.30:1 | AA large text | Lc 69.8 | Content text, not long reading |
| #637D91 text on black | 4.87:1 | AA | Lc -31.9 | 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
#F4F6F7
oklch(97.2% 0.003 228.8)
-
Step 100
100
#E7EAED
oklch(93.6% 0.005 247.9)
-
Step 200
200
#D3DAE0
oklch(88.5% 0.011 243.7)
-
Step 300
300
#B6C2CC
oklch(80.8% 0.019 243)
-
Step 400
400
#90A3B3
oklch(70.6% 0.032 243.6)
-
Step 500
500
#758DA0
oklch(63.1% 0.04 242.2)
-
Step 600
600 (this color)
#637D91
oklch(57.7% 0.043 241.6)
-
Step 700
700
#4D6476
oklch(49.2% 0.04 242.2)
-
Step 800
800
#3F5260
oklch(42.8% 0.033 240.5)
-
Step 900
900
#36444E
oklch(37.8% 0.025 239.4)
-
Step 950
950
#1F282E
oklch(27.1% 0.017 237.4)
#637D91 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) | #757D92 | 0.025 |
| Deuteranopia (no green cones) | #6F7891 | 0.020 |
| Tritanopia (no blue cones) | #558283 | 0.035 |
| Achromatopsia (no color) | #7A7A7A | 0.043 |
Harmonies
Hue rotations in OKLCH that keep this color's lightness and chroma.
Complementary
The opposite hue (180°).
- #637D91
#637D91
oklch(57.7% 0.043 241.6)
- #8D7460
#8D7460
oklch(57.7% 0.043 60.5)
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 #637D91, closest first.
Similar named colors
The eight closest entries in our named color list, with their ΔE distance.
- Grey Blue #647D8E ΔE 0.005
- Battleship Grey #6B7C85 ΔE 0.020
- Slate Gray #708090 ΔE 0.020
- Steel Grey #6F828A ΔE 0.027
- Stormy Blue #507B9C ΔE 0.029
- Battleship Gray #6C757D ΔE 0.033
- Steel #738595 ΔE 0.033
- Cerulean #457B9D ΔE 0.039
Use #637D91 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.