Defined Tideway
Defined Tideway (#51BEF2) is a true cyan with a neon character. It sits at the high-saturation edge of its family. Use it sparingly, as signage, accent, or highlight against darker surfaces. Its HSL profile (199°, 86%, 63%) places it in the highly saturated band at a mid 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 orange. For something softer, pull in its analogous neighbors on either side of the wheel.
Etymology
Latin dēfīnīre, to set bounds — past-participle of define. As a color modifier, defined implies a clear-and-edge-distinct-and-precise quality where the hue carries the visual register of sharp-bounded-and-clearly-delimited surface. Sits at the crisp-and-clear end of the grid, parallel to crisp and sharp in usage.
A tidal river channel — particularly the tidal Thames between London Bridge and Teddington Lock, the historical Tideway of London's Thames-side commerce. Tideway color refers to mid-tide Thames at Greenwich on a clear day: a soft, slightly cool deep blue-green with the optical complexity of tidal-mixed brackish water.
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.