  In trichromats, color vision entails the projection of an
infinite-dimensional space (the one containing all possible electromagnetic
power spectra) onto the 3-dimensional space that modulates the activity of the
three types of cones. This drastic reduction in dimensionality gives rise to
metamerism, that is, the perceptual chromatic equivalence between two different
light spectra. The classes of equivalence of metamerism are revealed by
color-matching experiments, in which observers adjust the intensity of three
monochromatic light beams of three pre-set wavelengths (the primaries) to
produce a mixture that is perceptually equal to a given monochromatic target
stimulus. Here we use the linear relation between the color matching functions
and the absorption probabilities of each type of cone to find particularly
useful triplets of primaries. As a second goal, we also derive an analytical
description of the trial-to-trial variability and the correlations of color
matching functions stemming from Poissonian noise in photon capture. We analyze
how the statistical properties of the responses to color-matching experiments
vary with the retinal composition and the wavelengths of peak absorption
probability, and compare them with experimental data on subject-to-subject
variability obtained previously.
