Obsidian Rhine
Obsidian Rhine (#051F3C) 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 (212°, 85%, 13%) 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 orange. For something softer, pull in its analogous neighbors on either side of the wheel.
Etymology
Volcanic glass — molten rhyolite cooled too quickly to crystallize. Mined since the Stone Age for blade-edges (sharper than surgical steel) and ground into mirrors by the Aztec priesthood for divination. The color refers to a polished obsidian flake from Mount Hekla or Glass Buttes, Oregon: a deep, slightly blue-shifted black with the high-gloss conchoidal fracture of natural glass. Cooler than onyx, glossier than coal.
The Rhine River — Europe's third-longest, flowing from the Swiss Alps to the Dutch North Sea. Rhine color refers to mid-depth Rhine River water at Lorelei on the Mittelrhein: a saturated, slightly cool deep blue with the optical depth of Alpine-glacier-fed European river water.
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.
Wide gamut
The CSS Color 4 wide-gamut form of this color. Both swatches render the same color on every display — the P3 form only diverges from sRGB when a designer pushes channels outside sRGB's reach.
This color sits well within the sRGB cube. P3 and sRGB share the gray axis and most desaturated tones, so a P3 display renders this identically to an sRGB display.