In 2013, Pridmore argued that most Red-Green cells reported in the literature in fact code the Red-Cyan colors. Thus, the cells are coding complementary colors instead of opponent colors. Pridmore reported also of Green-Magenta cells in the retina and V1. He thus argued that the Red-Green and Blue-Yellow cells should be instead called "Green-magenta", "Red-cyan" and "Blue-yellow" complementary cells. An example of the complementary process can be experienced by staring at a red (or green) square for forty seconds, and then immediately looking at a white sheet of paper. The observer then perceives a cyan (or magenta) square on the blank sheet. This complementary color afterimage is more easily explained by the trichromatic color theory than the traditional RYB color theory; in the opponent-process theory, fatigue of pathways promoting red produce the illusion of a cyan square.