Purpose: Adaptation to a steady background has a profound effect on both color appearance and discriminability. We wished to determine whether the time course of adaptation is the same for appearance and discrimination, and whether the temporal characteristics are identical along different color directions. Methods: Subjects were adapted to a large uniform background made up of a crt screen and a 60 x 60 deg wall illuminated by computer controlled neon lamps. After an instant change in background color, which could be along the L-M or S-(L+M) cardinal axes, we measured thresholds for the detection of increments or decrements along the same axes at fixed times between 500 ms and 120 s. Analogously, color appearance was determined during the same time interval using achromatic matching. The stimuli in both tasks had the same spatiotemporal characteristics. The fast phase of adaptation was measured in separate experiments, where the onset of the stimuli was between 8 and 500 ms after the background changed. In these trials, readaptation to the reference background occurred after each stimulus presentation. Results: Three different temporal components can be separated. We found a slow exponential increase of adaptation with a half-life of 25-30 seconds that was common to appearance and discrimination. However, the initial fast phase of adaptation was markedly different for appearance (half-life faster than 10 ms) and discrimination (approx. 200 ms). There were no differences for adaptational changes along the L-M and S-(L+M) cardinal axes. Conclusions: We conclude that the fast adaptation mechanism for color appearance is of higher order and situated after the mechanisms mediating slower adaptational changes in color discrimination and appearance.