Core Kuronezu
Core Kuronezu (#04083B) is a deep blue 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 (236°, 87%, 12%) 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 yellow. For something softer, pull in its analogous neighbors on either side of the wheel.
Etymology
Old French cor, heart / center — adjectival usage of core. As a color modifier, core implies a neutral-and-central-and-essential quality where the hue carries the visual register of Bauhaus-and-Mondrian-De-Stijl central-and-essential-design foundational-element-and-base-color. Sits at the neutral-and-foundational end of the grid, parallel to central and essential in usage.
Japanese 黒鼠, black-mouse — the deepest of the nezu (mouse-gray) family, a mid-Edo-period charcoal-and-iron-mordant color used in samurai-class everyday cotton. Kuronezu color refers to a samurai-class kuronezu-overdyed Edo-komon fine-pattern cotton: a dark gray with the matte finish of multi-bath charcoal-and-iron-mordant overdye on commoner cotton. Slightly cooler than Ainezumi.
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.
Moderately saturated colors gain a small bump in P3 — the difference is usually visible side-by-side on wide-gamut hardware but won't change the character of the color.