This is the back of my tent 185) the black layered has these spots notice none of the white has it? The front shows none of these spots on either the black or white.

Cleaned with warm water, vinegar & dawn platinum soap with a scrub. Was scrubbing deep and in circles. Not sure if it’s the seam just showing or if it’s mold. It didn’t smell or anything when I grabbed it out of my bag. Help