How come my eye colour is different in each eyes and changes?

Lately I’ve been looking deep into my eyes in the mirror. It turned out that my right eye is deep brown which is the colour I have thought my eyes have been my whole life. But I noticed a few things in my left eyes. 1: The eye has a giant green patch towards the bottom of it. 2: There is a little black spot towards the edge of my iris in the iris. The next day I looked at my left eye again and the green patch was bluer than before. It has been changing colours from shades of brown, blue and green for a while now. Is this normal? Or is it a rare condition? Or what?