1) Amorphous, nonproteinaceous pigment responsible for the brown hue of eyes, skin, hair, various tumors, and certain internal structures including the substantia nigra of the brain.

2) Pigments causing darkness in skin, hair, feathers, etc. They are irregular polymeric structures and are divided into three groups: allomelanins in the plant kingdom and eumelanins and phaeomelanins in the animal kingdom.

3) The substance that gives color to skin and eyes.