Fundamental Tetsu
Fundamental Tetsu (#160C33) 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 (255°, 62%, 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 fundāmentum, foundation — adjectival suffix -al. As a color modifier, fundamental implies a neutral-and-foundational-and-essential quality where the hue carries the visual register of Bauhaus-and-Mondrian-De-Stijl foundational-and-base-color theoretical-design fundamental-essential-element. Sits at the neutral-and-foundational end of the grid, parallel to foundational and essential in usage.
Japanese 鉄, iron — adopted into Japanese color terminology as the deep iron-gray of tetsubin cast-iron tea-kettles and tatara-furnace pig-iron. Tetsu color refers to a freshly tetsubin-cast iron tea-kettle exterior in raking light: a dark cool-gray with the matte finish of cast-iron-and-iron-tannin patina on hand-cast Nambu-tekki iron-ware.
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.