I'm wondering if this is some kind of fungus starting off. It's the same colour as his skin only brighter, with a dark rim.
Can be lot of things, but too me it look like he is gonna shed soon! Keep an eyes on the evolution! it can also be a burn (small light burn can have this light coloration) i doubt about the fungus/dermatits because its usually more yellow ish, brown or black.Pics here