Before revision:  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. Moreover, previous studies have shown that there is a certain trial-to-trial and subject-to-subject variability in the color matching functions. So far, no theoretical description has been offered to explain the trial-to-trial variability , whereas the sources of the subject-to-subject variability have been associated with individual differences in the properties of the peripheral visual system.
After revision:  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 , whereas the sources of the subject-to-subject variability have been associated with individual differences in the properties of the peripheral visual system.