Rhodopsin is a pigment present in the rods of the retina and belongs to a group of photoswitchable opsins. These are extremely sensitive to light, enabling low-light vision with a photobleaching effect.
Melanin is the pigment that gives colour to the skin. Retinol is the other name for vitamin A. Melatonin is the hormone released from the pituitary gland to maintain diurnal rhythm.