Before revision:  The classes of equivalence of metamerism is revealed by color-matching experiments, in which observers equalize a monochromatic target stimulus with the superposition of three light beams of different wavelengths (the primaries) by adjusting their intensities. The linear relation between the color matching functions and the absorption probabilities of each type of cone is here used to find the collection of primariesthat need to be chosen in order to obtain quasi orthogonal, or alternatively, almost-always positive, color-matching functions.
After revision:  The classes of equivalence of metamerism is revealed by color-matching experiments, in which observers equalize a monochromatic target stimulus with the superposition of three light beams of different 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 is here used to find the collection of primariesthat need to be chosen in order to obtain quasi orthogonal, or alternatively, almost-always positive, color-matching functions.