This page explains how every number on the site is produced, which standards it follows, and where its limits are. The point is to let you judge whether a result is safe for production, not to ask you to trust us.
Where the color values come from
Traditional colors are given as commonly used sRGB approximations drawn from public color-name references and surviving reproductions. They are not claimed to be the single correct value: the same “ai” indigo differs between dye houses and between centuries. Every derived format (RGB, HSL, HWB, Lab, LCH, OKLCH, XYZ, LUV) is converted from that one sRGB triple using CSS Color 4 formulas with fixed rounding, so the same color shows identical numbers everywhere. We do not read your display profile and do not calibrate monitors.
How contrast is calculated
Per WCAG 2.x: linearize each channel, compute relative luminance (0–1), then apply (L1+0.05)/(L2+0.05) for a ratio between 1 and 21. Transparency, overlaid imagery and gradients are not part of the calculation, so the number is “ratio between two solid colors”. If your interface uses translucent scrims or photographic backgrounds, measure the final rendered pixels again.
ΔE, or how close two colors are
We report both ΔE76 (CIE76, Euclidean distance in Lab) and ΔE OK (the OKLab variant). The former is old enough to compare against other tools; the latter is more perceptually even in lightness and hue, which makes it better for deciding whether a difference is visible. As a rule of thumb ΔE OK below 0.02 is essentially indistinguishable, 0.02–0.05 needs a side-by-side comparison, and above 0.05 is clearly different. These are heuristics, not standard thresholds.
CMYK and print
CMYK values are converted with the Coated FOGRA39 profile for communication and approximation — not as a soft proof. Emissive screens and reflective paper behave differently, and the same CMYK numbers shift noticeably on uncoated stock, newsprint or another press. For real print work, rely on your printer’s profile and a physical proof.
Traditional names and cultural attributes
Japanese entries draw on JIS customary and traditional color names; Chinese entries on the national color system and on historical textile and pigment names; Korean and Vietnamese entries on local name references. Names stay in their original script (藍, 群青, 송화, thủy) because a translated color name is no longer that name. Attributes such as season or five-element association reflect common usage rather than a single reading, and entries still under review are labelled as such.
Corrections and updates
Report errors to steve@irodori.cool with the page URL and your evidence (a reference, a photograph of a physical sample, or a standard number). We normally reply within three business days. Confirmed corrections are recorded in the changelog, and the page’s “last updated” date and schema dateModified are updated with them. Uncertain changes are not published just to look tidy.