He is probably losing a little pigment on the iris making them a little more pale and less vibrant in color and the peripheral cornea near the limbus tends to collect some iris color is fading a little and gaining a slight bluish tint. The color of the iris is not changing however. It is totally totally normal is some people and nothing to be concerned about.
Yeah, I actually learned some interesting things from both an internet article, and a college class. The basic idea is that way back when, all people had Brown/black eyes. But the lighter gray/blue/green/etc eyes originated as a genetic deficiency of pigment in not just the Iris, but skin as well.
Don't ask me how the genetics caught on so well, but they did.
So yeah... as said, nothing to worry about. (Kinda interesting though)
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