Seasonal color analysis is usually explained with fabric drapes and words like "warm" and "soft". If you're a developer, it's easier to think about it as a small color-science problem. Disclosure up front: I'm part of the team that built DoColorAnalysis, a free online color analysis tool, so this is the mental model we found useful, not a sales pitch.

The four variables

Most 12-season systems reduce a person's coloring to four properties:

Undertone (hue direction) : is the skin leaning yellow/golden (warm), pink/blue (cool), or in between (neutral)?

Value (lightness) : how light or dark the overall coloring is.

Chroma (saturation) : are the hair, skin and eye colors clear and saturated, or muted and greyed?

Contrast : the lightness difference between hair, skin and eyes.

The seasons are just regions in that space. Spring is warm and clear, Summer is cool and soft, Autumn is warm and muted, Winter is cool and high-contrast.…