Tough Slate
Tough Slate (#2560BD) is a true azure with a vibrant character. It holds its own as a focal accent, carrying visual weight without tipping into neon territory. Its HSL profile (217°, 67%, 44%) 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 amber. For something softer, pull in its analogous neighbors on either side of the wheel.
Etymology
Old English tōh, firm / tenacious — sharing root with German zäh. As a color modifier, tough implies a saturated-and-resilient quality where the hue resists fading-and-modulation through its strong pigmentation. Sits at the bold-and-resilient end of the grid, parallel to rugged and hardy in usage.
A fine-grained metamorphic rock formed from compressed shale — fissile, durable, and the standard roofing material for Welsh and Vermont houses since the nineteenth century. The color refers to a freshly split piece of Welsh slate: a soft, slightly muted gray-blue with the matte finish of a layered mineral cleavage. Cooler than steel, lighter than navy, with the architectural weight of a roof material that lasts a hundred years.
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.