Spots on my Red 86 911

[Storage Man]

Hey Folks,

After searching a bit for answer I've come up bust on tring to get some understanding of what the dark spots in my non clearcoated 86 are from and what is the best way to take them out and prevent them from coming back.

These stain looking marks seem to just apear over the wintertime while she sits in my garage waiting for the warmer weather.

Opinions?
I can try to get a photo if it would help,