Plumb Cobaltite
Plumb Cobaltite (#18579B) is a true 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 (211°, 73%, 35%) places it in the balanced band at a mid lightness. It works across type, buttons, and borders, saturated enough to feel deliberate but balanced enough to not fight the rest of the palette. 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
Latin plumbum, lead — referring to the lead-weighted plumb-line of pre-modern carpentry. As a color modifier, plumb implies a clear-and-vertical-true quality where the hue carries the visual register of gravity-aligned-and-perfectly-vertical surface. Sits at the crisp-and-balanced end of the grid, parallel to level and squared in usage.
A cobalt-arsenic-sulfide mineral — the principal historical source of cobalt for ceramic and pigment use. Mined principally in Cobalt, Ontario (the source of the modern cobalt-mining industry's name). The color refers to a polished cobaltite crystal: a soft, slightly cool deep blue-silver with the metallic finish of crystallized cobalt mineral.
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.