Sullen Steel
Sullen Steel (#031B51) is a deep azure with a jewel character. It carries the deep, saturated richness of a gemstone. Authoritative and slightly formal, it works well for type and heavy UI elements. Its HSL profile (222°, 93%, 16%) places it in the highly saturated band at a dark lightness. Best used in small doses, like logos, CTAs, focus rings, or highlight text, where its saturation becomes a feature rather than noise. For a confident two-color system, pair it with its complementary amber. For something softer, pull in its analogous neighbors on either side of the wheel.
Etymology
Old French solain, solitary via Anglo-French solein. As a color modifier, sullen implies a deep-and-cool-and-withholding quality, the dark cool-gray of Norwegian-fjord mid-winter atmospheric-overcast and saturated-saltwater-cliff in late-November light. Sits at the deep-and-cool end of the grid, parallel to gloomy and saturnine in atmospheric tone.
An iron-carbon alloy hardened by heat treatment — and steel blue refers specifically to the blue oxide layer that forms on tempered steel as it's heated through 290°C, the temper colors a blacksmith reads to gauge the correct hardness. The color is the blue of a freshly tempered file: a soft, slightly muted gray-blue with the metallic finish of an oxidation layer. Cooler than slate, warmer than denim.
Closest matches
The nearest named color in three reference sources, ranked by perceptual distance (ΔE76 in CIELAB). ΔE < 1 is imperceptible to most viewers; ΔE > 10 is clearly different. When two sources point to the same hex they’re merged into one tile; click any to open that color’s page.
Variations
Click any swatch to exploreHarmonies
Accessibility
How this color appears to viewers with the four major color-vision-deficiency types. Computed via the Machado (2009) physiologically-based model. If a tile matches the original, the color reads the same to that viewer.
The color used as foreground text against pure white and pure black, with the contrast ratio and WCAG 2.1 grade. Aim for AA (4.5:1) for body text and AA Large (3:1) for 18 pt+ headlines; AAA (7:1) is the gold standard for long-form reading surfaces.