I normally have blue eyes, but sometimes they change to grey, what gives?

Hey all, I have blue eyes. Well, most of the time.

I notice them changing between three sort of phases, one is an extremely bright blue, very noticeable, the next is more of a pale blue, still blue but it doesn’t stand out as much.

And then the weird bit, sometimes my eye turn grey, and I don’t mean a little, I mean almost completely grey, and very cold.

Haven’t really narrowed down what moods I am in when they change but it certainly seems a bit strange. What can cause this? (I mean, it can be affected by mood probably, but scientifically, how?)