Youdontneedtoknow :
cryoburner :
If I had to guess, it looks like it could be some kind of fungus growing in there. It appears to be visible on other surfaces as well, like the motherboard heat sink to the right, some other components, and the board itself. Is this computer located in a humid location, or was it ever exposed to moisture?
In any case, it will likely require a thorough cleaning, perhaps a complete submersion in 90+% isopropyl alcohol.
Only thing i can think of is that i Used mayonaise as thermal paste for a very long time and it was the same color/look as the little spots on the motherboard. I will look into that alcohol method... maybe it is some type of fungus... but it accumilates in the pci slots so maybe its just that my graphics card is old HIS IceQ... im sad because a bitch is poor... im still troubleshooting atm with a friends computer
I have read about using that and it does seem to work, but it is only short term. Better to get actual thermal paste. Mayo can grow stuff, LOL. Knowing that, I think it might be yellow mold growing in there. Yeah, your best bet is to do as cryoburner suggested, do a complete submersion to try and take care of it. Your other components probably are fine as the mold would be growing on the your MB, but if left in long enough, it would spread to them, so take the components out and leave them all out until you have it taken care of.
Also, make sure you have proper ventilation through your case. Yellow mold like dark and damp. If you have proper air flow, it will keep the humidity out of your system and could help prevent future growth.