Like human eyes, dog eyes have a pigment called melanin (MELL-uh-nin) in the iris—the colored part of the eye. The iris has two layers. Brown eyes have melanin in the front and back layers. Lighter eyes have little or no melanin in the front layer and just a little in the back. (If no pigment is in either layer, the iris looks pink.) As an animal develops, genes in its DNA tell its body how much melanin to turn “on” or “off.” This means that animals can have a range of eye colors. The same is true for skin, hair, and fur colors.
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