Foundational Cobblestone
Foundational Cobblestone (#170B31) 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 (259°, 63%, 12%) places it in the balanced band at a dark lightness. It works well as a headline, icon, or deep background in an otherwise light layout, pairing cleanly with cream, bone, and warm neutrals. 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 fundātiō, foundation — adjectival suffix -al. As a color modifier, foundational implies a neutral-and-base-and-supporting quality where the hue carries the visual register of Bauhaus-and-Mondrian-De-Stijl foundational-and-base-supporting-color theoretical-color-system. Sits at the neutral-and-foundational end of the grid, parallel to primary and essential in usage.
Old English cobel, rounded river-stone — the iconic dark-gray paving stone of medieval-and-early-modern European cities, particularly the Rome and Edinburgh historic-center streets. Cobblestone color refers to a Roma centro storico sampietrini cobblestone pavement-section in raking sun: a dark cool-gray with the matte finish of basalt-and-leucitite volcanic-rock cobblestones polished by centuries of vespa-tire wear.
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.