In Experiment I, three groups of 20 Ss each were exposed to a light of 550 mmu (yellowish-green) for 60 sec and then viewed a random sequence of wavelengths with instructions to respond only to the original color. The instructions given the three groups were worded differently in an attempt to vary the strength of a set-to-discriminate assumed to be created by this procedure. The three groups produced similar gradients, each with a peak of responding at 540 mmu, in agreement with Kalish's (1958) published gradient for the 550 mmu standard stimulus value. It was suggested that the nature of the task is such that a strong discriminatory set is produced regardless of the wording of the instructions.A temporal analysis of the gradient as it develops during the testing revealed that initially the peak of responding occurs at 550 mmu; but as testing progresses, it shifts gradually in the direction of the shorter wavelengths (purer greens). Experiment II was performed to test the generality of the phenomenon of regression to the primary color. Two groups of 20 Ss each were tested for generalization following exposure to 510 mmu (bluish-green) and 525 mmu (pure green), respectively. We predicted that the 510 mmu gradient would reveal a progressive shift toward the longer wavelengths (purer greens), whereas the 525 mmu gradient would show no tendency to shift. The results were strikingly in accord with these predictions. We concluded that although a physiological process could not be ruled out, the verbal labeling of the standard stimulus value may well be responsible for the regression of the gradient toward the primary color.