Subject: What is the function of iris pigmentation?

I am a compuer scientist working in a laboratory full of biologists. I have
always been lead to believe that people with blue eyes have better night 
vision than brown-eyed people. Nobody in my laboratory believes me. This
got me reading up on the subject, I became more interested in the general
function of iris pigmentation. I know how the iris regulates the amount of
light entering the eye by controlling the size of the pupil, but what role
does the colour of the iris play is in this process? I am also interested 
in the nature of the pigmentation itself. I know that the epithelial layer
of cells at the back of the iris is pigmented with melanin, but what is the
nature of the pigment in the front part of the iris?

Re: What is the function of iris pigmentation?