Can anyone explain the mechanics of hazel eyes to me?

I have hazel eyes and I've always been one to want to know how things, especially physiological, work but don't really understand how eye coloring works. For example, I've noticed that in regular lighting and on most occasions my eyes are a light or medium brown. When I'm outside and it's a dreary overcast day my eyes are a very light brown with a yellow tinge. When it is a very sunny, practically cloudless day my eyes are a bright emerald green color. Then, when I'm in a room with fluorescent lighting my eyes are a pale/olive green with a noticeable brown ring around the pupil and can sometimes have yellow/gold flecks in them. Also, if my eyes become watery or I've been crying my eyes turn that emerald green color. Can anyone explain how hazel eye coloring actually works? Is it simply because of light reflection or is there something more to it?