Hazel eyes are due to a combination of Rayleigh scattering and a moderate amount of melanin in the iris' anterior border layer.Hazel eyes appear to shift in color from a brown to a green. Although hazel mostly consists of brown and green, the dominant color in the eye can either be brown/gold or green. This is how many people mistake hazel eyes to be amber.This can produce a multicolored iris,that is light brown/amber near the pupil and charcoal or dark green on the outer part of the iris.
[VIDEO] RAYLEIGH SCATTERING explained by Professor Emeritus Walter Lewin at MIT (and more) For The Love Of Physics. I recommend watching the whole lecture from beginning, the part on color starts at about 28:00 http://youtu.be/SRh75B5iotI?t=27m56s
“ This is a deep image of the Sword of Orion - the three stars that make up the weapon hanging off the belt of this famous celestial hunter. The image showcases the amazing mix of physical and optical.