The opponent process theroy of color vision recommends that our capacity to perceive color is constrained by three receptor complexes with contradicting or opposing activities.
These three receptor complexes are as follows:
Dark white complex.
Blue-yellow complex.
Red-green complex.
You don't see greenish-red because according to the opponent process theory, the opponent cells can just identify each of these colors at a time.
B. Mutations cause a person's body cells to divide uncontrollably. There isn't a signal for cells to stop dividing, so this can cause cancer because cancer cells won't stop dividing without this signal.
