Contrast level
The visible gap in lightness between your hair, skin and eyes, from low and blended to high and dramatic.
Contrast level measures how far apart your hair, skin and eyes sit from each other in value once color is stripped away, essentially how they would look in a black-and-white photograph. Someone whose hair, skin and eyes are all similar shades of light or medium tone reads as low contrast; someone with very light skin and very dark hair reads as high contrast. Contrast is closely tied to value and chroma and is one of the most useful home tests in color analysis, because it can be checked fairly objectively with a desaturated photograph rather than judged by eye against colored swatches. It also explains why two people in the same season can look different: contrast decides how boldly a palette should be combined, with low-contrast coloring generally suiting tonal, blended outfits, while high-contrast coloring can carry sharp color-blocking and stronger neutrals like black or white without looking harsh.
Why it matters
Contrast level is the tie-breaker between light and deep neighbouring seasons and the single most reliable home measurement available, since it does not depend on judging color by eye at all, only on comparing greyscale values in a plain photo taken at home.