I know that human eye can change its color during lifetime because of disease or medication (similar question on Biology.SE). And I know that it may change depending on the lighting.
But I saw several times as the eyes of man with the bright eyes changed color (blue/gray/green) without changing environment. Is it possible to temporarily change eye color due to the change of emotional state (as a consequence of the effect of hormones or something else) in just a few of minutes? If so, what are the processes behind this?
Or it just optical/psychological illusion for the observer?