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How do the three types of cone cells in the retina help humans distinguish colours?

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A circular RYB color wheel divided into twelve segments, showing a progression of colors from red, orange, and yellow to green, blue, and violet. — colour The RYB color model is being illustrated on a color wheel.

Humans distinguish colours through the trichromatic theory, which relies on three types of cone cells in the retina. These cones are categorized by their sensitivity to different wavelengths of light: short (S), medium (M), and long (L).12

Each cone type contains a distinct photopigment that responds maximally to specific regions of the spectrum:
* S-cones: Sensitive to short wavelengths (blue-violet, peak near 445 nm).31
* M-cones: Sensitive to medium wavelengths (green, peak near 535 nm).31
* L-cones: Sensitive to long wavelengths (red, peak near 565 nm).31

When light enters the eye, it stimulates these receptors with varying effectiveness. The brain interprets the resulting pattern—specifically the ratio of excitation across the three cone types—to perceive a wide range of hues. While the trichromatic system explains how initial signals are generated, these signals are further processed in the brain into opponent channels (light–dark, red–green, and blue–yellow) to refine our perception of colour.321