Courteous Kuroshio
Courteous Kuroshio (#040628) 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 (237°, 82%, 9%) 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 cortois, of-the-court — adjectival suffix -ous. As a color modifier, courteous implies a neutral-and-formal-and-polite quality where the hue carries the visual register of Edwardian-and-Belle-Époque formal-and-courteous-of-the-court interior-decoration-and-dress-attire coordinated-color tone. Sits at the neutral-and-friendly end of the grid, parallel to mannerly and polite in usage.
Japanese 黒潮, black current — the warm-water Pacific Ocean current that flows northeast along Japan's eastern coast, named for its deep blue-black color compared with the cooler greener offshore waters. Kuroshio color refers to a deep-water Kuroshio current surface in clear weather: a saturated, slightly cool deep black with the optical complexity of deep-water Rayleigh-scattered light through a thousand-meter water column.
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.