Rudimentary Penumbra
Rudimentary Penumbra (#180027) is a deep indigo 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 (277°, 100%, 8%) 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 lime. For something softer, pull in its analogous neighbors on either side of the wheel.
Etymology
Latin rudīmentum, first principle — adjectival suffix -ary. As a color modifier, rudimentary implies a neutral-and-basic-and-stripped-down quality where the hue carries the visual register of prehistoric-and-cave-art rudimentary-and-foundational-mineral-pigment color-decision. Sits at the neutral-and-foundational end of the grid, parallel to basic and primal in usage.
Latin paene-umbra, almost-shadow — the partial-shadow outer cone of an eclipse shadow, where the occulting body partly blocks the light source. Penumbra color refers to the partial-solar-eclipse deep gray shadow-cast on the ground: a saturated, slightly cool deep black with the optical complexity of partial-solar-eclipse atmospheric scattering against a shadow-cone-partially-occluded sun-disk. Slightly less dark than umbra.
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.