Color methodology

The Color cluster handles conversions between four representations of the same underlying colour: HEX (#FF6B35), RGB (255, 107, 53), HSL (16°, 100%, 60%), and HSV (16°, 79%, 100%). All four describe a colour in the same colour space — sRGB — so the conversions are algebraic relabelings, not perceptual remappings.

sRGB as the universal anchor

sRGB (Standard RGB) is the default colour space of the web, defined by the IEC 61966-2-1 standard in 1999. It specifies the exact red, green, and blue primaries that combine to produce any displayable colour, plus a non-linear gamma curve approximating the response of a typical CRT monitor. Modern LCDs and OLEDs emulate this curve.

Every HEX colour, every rgb(…) value, every CSS-default hsl(…) assumes sRGB unless otherwise tagged. Newer wide-gamut formats (Display P3, Rec.2020) exist but require explicit opt-in via color(display-p3 …)or similar — outside this cluster’s scope.

The conversion math

HEX ↔ RGB

Direct base conversion: each pair of hex digits is one byte (0-255). #FF6B35 ↔ rgb(255, 107, 53) exactly, no precision loss. Three-digit hex (#F63) is the shorthand for #FF6633.

RGB → HSL

Convert R, G, B to the range [0, 1]. Find the max and min channels. Lightness L = (max + min) / 2. Saturation depends on whether L < 0.5 or not. Hue is computed from which channel is the max and the relative differences between channels.

The full formula is standard and is implemented exactly in our library. Hue is reported in degrees [0, 360); saturation and lightness in percent [0, 100].

RGB → HSV

Similar logic. Value V = max. Saturation S = (max − min) / max when max ≠ 0. Hue is identical to the HSL hue.

HSL and HSV diverge on the saturation axis. A colour at 100% HSV saturation is fully saturated; at 100% HSL saturation it’s fully saturated only at L = 0.5. Designers prefer HSL for adjusting tints and shades; image editors often expose HSV (Photoshop calls it “HSB” for “brightness”).

Round-trip precision

HEX ↔ RGB is bit-exact. Either direction round-trips losslessly.

RGB ↔ HSL / RGB ↔ HSV involve floating-point arithmetic. Round-trip precision is bounded by the 8-bit RGB output — the worst case rounds a channel by ±1 out of 255 (about 0.4%). Display-wise this is invisible; for colour-critical work avoid the round-trip if you can.

Algorithm details: HSL and HSV in full

The conversion library ships these formulas verbatim; they’re reproduced here so the algebra is visible. Normalised inputs R, G, B ∈ [0, 1] with M = max(R, G, B), m = min(R, G, B), chroma C = M − m:

L = (M + m) / 2
S_HSL = C / (1 − |2L − 1|) if C ≠ 0, else 0
V = M
S_HSV = C / M if M ≠ 0, else 0

Hue is the same axis in both models:

H = 60° × ((G − B) / C mod 6) if M = R
H = 60° × ((B − R) / C + 2) if M = G
H = 60° × ((R − G) / C + 4) if M = B

The sRGB linearisation, applied when computing luminance for contrast or interpolating perceptually, is the piecewise transfer from IEC 61966-2-1: linear = c/12.92 if c ≤ 0.04045, else ((c + 0.055)/1.055)^2.4. Round-tripping through linear and back is bit-exact for the 8-bit sRGB grid because the piecewise inverse is well-defined.

Sources & references

Every formula on this page is from a primary spec or a peer-reviewed publication: sRGB primaries and gamma from IEC 61966-2-1, CSS hex/rgb/hsl syntax from W3C CSS Color Module Level 4, RGB↔HSV conversion from Smith’s 1978 paper, contrast formula from WCAG 2.2. The Sources block at the foot of this page lists the publicly-available versions used as ground truth during library testing.

Assumptions & limitations

• sRGB throughout.Inputs without an explicit colour-space tag are assumed sRGB. P3 / Rec.2020 / Adobe RGB inputs aren’t auto-detected and would be misinterpreted if passed as raw RGB.
• 8-bit integer RGB. Hex input clamps to [0, 255] per channel. 10- or 12-bit HDR pipelines need a wider format than #RRGGBB.
• HSL/HSV are convenience reparameterisations, not perceptual spaces.Equal numeric changes in H, S, or L don’t map to equal perceptual changes — use OKLCH or CIELAB for perceptually-uniform work.
• No chromatic adaptation.Converting across spaces with different white points (D65 ↔ D50) requires a Bradford or CAT02 transform we don’t apply.
• CMYK requires ICC profiles.Algebraic CMYK ≈ RGB approximations on the web are uniformly wrong for print; we don’t emit a CMYK value at all.
• Alpha is passthrough, not premultiplied.Round-tripping through HSL/HSV preserves the alpha channel but doesn’t apply the alpha to the colour components.

What we don’t handle

• Wider-gamut spaces (P3, Rec.2020) — out of scope.
• Perceptually-uniform spaces (Lab, LCH, Oklab) — sometimes asked for; the algebra is more involved. May ship as a separate tool later.
• CMYK — print-specific colour space; conversions require ICC profiles, not just algebra. See our RGB vs CMYK comparison.
• Alpha — RGB→HSL/HSV preserve alpha as a passthrough. HEX with alpha (#RRGGBBAA) is supported.