It has to do with SOMEthing, I'm quite sure.

Here's something I found:

You may have noticed that some animals’ eyes reflect light at night. Deer, cats, crocodiles and even moths have eyes that do this and it’s because they have a tapetum. A tapetum is a reflector at the back of the eye that effectively doubles the amount of light the eye can use, helping an animal to see at night. Humans don’t have a tapetum. The only time their eyes seem to reflect light is when they look red in some pictures. This is just the camera flash bouncing off the red tissue in the back of your eye.
source: http://www.healthyeyes.org.uk/index.php?id=83

I'm assuming after it is reflected off the tapetum the color has to go back through the eye and eye color MAY affect it (but if you've looked, its always the pupil that refelcts the light and not the actual iris itself.