[Color adaptation in a yellow-blue system: proof of a simple numerical relationship].

Three axes in color space are specified: a (unique) yellow - (unique) blue axis, a (unique) green - magenta axis and brightness. Based on the two chromatic axes two linear opponent colors systems are defined: a red/green-system and a yellowish/bluish-system. A numerical relation is presented to describe color adaptation for the yellowish/bluish-system under adaptation to (unique) yellow and (unique) blue: two pairs of color stimuli are equivalent with regard to the yellowish/bluish-system - consisting of a test stimulus and an adaptation stimulus, respectively - if the ratios from the yellowish/bluish-coordinates of test stimulus and adaptation stimulus are identical. A control of brightness and the red/green-system is presupposed. For several (unique) yellow and (unique) blue adaptation stimuli it is examined how a test stimulus that appears neither yellowish nor bluish changes its location on the (unique) yellow - (unique) blue axis within color space. Three observers take part in the experiment. For each observer a plane of constant brightness and the opponent colors axes are estimated experimentally. The data show that the ratios from the yellowish/bluish coordinates of test stimulus and adaptation stimulus are essentially constant. The results are compared with analogous data for the red/green-system. The findings provide evidence for the specification of the three phenomenal axes. The specification is discussed with regard to Hering's opponent colors theory and Krauskopf's three "cardinal" axes [1982, Vision Research, 22, 1123-1131].