Color, Depth and Undertone
Depth is one axis and undertone is another, and most shade guides only know the first. Shade matching, why the standard undertone tests fail, and what to do when the foundation you own looks ashy, orange or gray.
Two axes, not one. Depth runs light to deep and undertone runs green to red, and confusing the two is why a foundation can be the right darkness and still look wrong. How skin tone is actually measured covers the difference between the scales, including the one most beauty writing borrows for the wrong purpose.
Olive gets treated as a real category here rather than a footnote, because it sits on the green side of an axis most shade ranges decline to acknowledge, which is precisely why the usual vein and jewelry tests fail on it.
How Skin Tone Is Measured: The Scale Beauty Uses Was Built for Sunburn
How skin tone is measured, and why the Fitzpatrick scale cannot answer a shade-matching question. It classifies sun reaction, not color, and it says so.
10 min readWhy Undertone Tests Fail: The Vein, the Paper, and the Jewelry
Undertone tests using veins, white paper or gold jewelry each measure something real. None of the three measures undertone, and here is what each one tracks.
10 min readOlive Undertone: The Axis the Standard Measure Leaves Out
An olive undertone is not a point between warm and cool. It sits on a third color axis, and the standard skin-tone measure is calculated without that axis.
9 min readFoundation Shade for Deep Skin: What the Research Skipped, and What It Found
Foundation shade matching for deep skin has been understudied, and the paper that says so also found deeper shades drift less than lighter ones on the product.
10 min readFoundation Oxidizing: The Darkening Is Real, the Name Is Wrong
Foundation oxidizing is a real effect with a misleading name. When the causes were measured, sebum dominated and light barely mattered. What follows.
10 min read