It is a curious detail that a side effect of raw food diets is the change in eye colour. It has been reported along with claims that their eyes become ‘clearer’, and that their vision actually improves somewhat. This is purportedly due to the internal cleansing effect of a raw food diet, improving circulation. It usually takes several months for the colour change to become prevalent, yet only a mere few weeks for the improvement in clarity of vision.

This consequence is mentioned pithily in Viktoras Kulvinskasbook of letters “Life in the 21st Century”. In the iridology section it cites that “as the body regenerates. The iris changes in colour value… With healing, the natural colour will return. The whole iris may become lighter in colour.”

Some people's eye colours may be ‘set’ by genetics , and in those people the eyes become clearer, but the colour quality might not change. The Ayurvedic view of eye colour is that your eyes are the colour that you have in "excess" (namely, in the astral or spiritual body). That view supports the idea that changes in eye colour may be possible due to the deep cleansing provided by a raw food diet.

More interestingly, there are cases of Multiple Personality Syndrome in which a person's eye colour changes according to which personality is occupant at the time! There have also been fairly recent newspaper reports about a drug approved by the FDA that has the “side-effect” of changing your eye colour. So, there is considerable evidence to support the idea that eye colour can change.

Further evidence for the idea that eye colour can change in presented in the book, "Aghora: At the Left Hand of God", which presents a description of the life and principles of a Tantric expert, named Vimalananda. In the introduction, Svoboda speaks of Vimalananda:

"He certainly was not confined by the restrictions which confine most mortals. His eyes, for example, refused to remain the same colour at all times. Sometimes they were a light blue, often they were light green, the colour of a grape known as anab-e-shahi. At some moments they could become nearly colourless....At other times when he was feeling playful he would adjust his eye colour to match mine and would then call everyone in the room over to see and comment..."

Obligatory disclaimer, due to numerous (and sometimes heated) complaints: I am not claiming absolute authority over this topic. I am simply re-stating some of the ideas i have read in several health oriented books which names elude me.