Subject: Why do irises change color?

My boyfriends eye iris color changes periodically - both eyes are brown most of
the time but can change to green.  I first noticed this 7 months ago, and have
since discovered his eyes change in natural light and indoors, there's no
(obvious) pattern or reason.  When I searched the net on this topic, I saw a
similiar question - wondering if anyone has more info?  The answer given by
Kenton McWilliams (ref: May 30 20:57:32 2004) doesn't really solve this as my
boyfriend is 26 years old.  So anyone know why his iris can go from green to
brown to green?

Re: Why do irises change color?