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Why can a single perceived colour result from more than one combination of light beams?

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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.

A single perceived colour can result from different combinations of light beams due to a phenomenon known as metamerism.12

This occurs because human colour vision is based on the stimulation of three types of photoreceptor cells in the retina called cones, which are sensitive to short (blue), medium (green), and long (red) wavelengths. The brain interprets perceived colours based on the ratio of excitation among these three cone types.3

Because the eye reduces complex spectral information into these three signals, different physical spectral compositions can trigger the exact same ratio of excitation in the cones. When this happens, the brain perceives the two different light combinations as identical in colour. This is why, for example, a specific shade of yellow can be produced by a single spectral wavelength or by a mixture of red and green light beams. Because of metamerism, two objects that appear to match under one light source may look different under another, as the spectral energy distribution of the illumination changes how the objects reflect light.13452