The "before" pic looks like you were growing mold.
Back in the 80's, I had a Grand Prix that had a white vinyl half-top. It just covered the rear of the roof. I had it re-dyed after maybe 4-5 years because it got to looking dirty. It looked good for about 2 years after that, then I traded it in.
Apparently white is tought to keep clean, but mine was never in a garage either.
Mike