Same swatches, same voxels, different metric
Choosing where to project a skin color barely matters: every admissible axis ranks the observations the same way (Spearman ρ ≥ 0.992). What decides the quality of a measurement is the space you compute in. This page shows the two places CIELab breaks down on the skin manifold — and neither is a rounding error.
← Back to the methodology walkthroughNearest-swatch assignment degenerates in CIELab
Both panels show the same 8,738 observed voxels and the same ten official Monk swatches, in the same L*–b* projection. The only difference is the distance used to decide which swatch owns which region. Under CIELab, MST 3 is squeezed into a sliver holding 0.48% of the voxels while its neighbor MST 2 swells to 8.77% (red borders). Under RGB, the cells track the elongated axis of the skin band and the categories recover coherent shares.
The swatches are not monotone in L*
This one needs no data at all — just the ten official swatches. They increase monotonically in RGB brightness, but not in CIELab lightness: MST 3 is lighter than MST 2 in L*, differing from it mainly in yellowness. A scale that is ordered in one space and disordered in another is telling you something about the space.
| MST | Hex | RGB brightness | L* | b* |
|---|---|---|---|---|
1 | #f6ede4 | 0.071 | 94.1 | 5.0 |
2 | #f3e7db | 0.094 | 92.2 | 7.0 |
3 | #f7ead0 | 0.099 | 93.3 | 14.0 |
4 | #eadaba | 0.166 | 87.5 | 18.0 |
5 | #d7bd96 | 0.276 | 78.0 | 23.0 |
6 | #a07e56 | 0.514 | 55.3 | 27.0 |
7 | #825c43 | 0.622 | 42.4 | 20.0 |
8 | #604134 | 0.722 | 30.6 | 13.0 |
9 | #3a312a | 0.805 | 21.2 | 6.0 |
10 | #292420 | 0.858 | 14.5 | 4.0 |
RGB brightness = 1 − mean(R,G,B); larger is darker. Monotone top to bottom. L* is not.
ITA° saturates at the light end
ITA° takes an arctangent, and near the light end of the band it compresses: genuinely distinct pale tones collapse into a few degrees of angle. Between the two lightest Monk categories, ITA° separates at Cohen's d = 0.013 — a coin flip — where the linear RGB index reaches d = 2.90.
One dot per observed voxel, painted with its own color. The ridge is monotone; the fan-out at the left is the saturation.