Undertone

Undertone is separate from how light or deep a colour is. Two people with the same skin depth can have different undertones, and two red lipsticks with the same lightness can lean in opposite directions.

For skin, undertone is usually described as cool (pink, red or bluish), warm (golden, peach or yellow) or neutral (a balance of the two). Olive skin is often described separately because of its green or muted cast.

For a lipstick, this encyclopedia assigns undertone from the shade’s measured hue angle: shades that lean toward blue are cool, true reds are neutral, and shades that lean toward orange or yellow are warm. The exact ranges are on the methodology page.

A common colour-theory guideline pairs a shade with skin of a matching or neutral undertone: cool-toned shades suit cool and neutral skin, warm-toned shades suit warm and neutral skin, and neutral shades suit all three. It is a starting point, not a rule.