Hazel eyes are one of the least understood eye colors. This color is semi-rare and is a combination of several other colors including green and brown. Hazel eyes have less melanin than brown eyes, but more than blue eyes. Hazel eyes often appear to shift in color from brown to green. Hazel eyes are a combination of Rayleigh scattering, the principle that makes the sky and blue eyes appear blue, and melanin, the pigment that makes brown eyes brown.