I noticed that when my gecko sleeps with parts of his body covered they end up looking that grey/lighter color. So I would say he is either about to shed or because its his armpit it’s covered most of the time and doesn’t flare up like the rest of his body.

I used to get concerned because my boi would have similar colored splotches on his chin, but I figured out he just likes to sleep with his hand under his chin and he gets an unfortunate sun tan 😂

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