Small grey dots on case

[Leonidas199x]

Hi,

I have recently noticed 6 small dots (about the size of a pin head and almost perfectly circular) on the case of my macbook.

They are near the light up apple.

I have taken my macbook to Apple and they have said it is cosmetic and cannot help me, but I fail to see how I could have created these dots as they appear to be discolouration in specific places.

Does anyone have any idea what could cause them, I haven't spilled anything on it and it hasn't been in any extreme conditions?

Thanks