Plain Tideway
Plain Tideway (#18535F) is a deep cyan 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 (190°, 60%, 23%) 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 red. For something softer, pull in its analogous neighbors on either side of the wheel.
Etymology
Latin planus, flat, level — used as a color modifier since the medieval period for hues that read as undecorated and direct. Plain white, plain blue: moderate saturation, no shift, no surface effect. Sits in the crisp-bucket center, with the implication of restraint rather than absence.
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.
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.