We spent much of this past winter in cold weather climates and that area was one of the first we noticed the mold stains. We tried vinegar as well as many other products, but the only one that worked for us on that material, in a timely fashion, was Tilex
(which contains a significant amount of bleach). Spray it on with a good deal of ventilation and wait a few hours. Dry the area with a fan to get rid of the bleach odors. Repeat if necessary. That material is colorfast but the bleach will lighten the color
a bit as it bleaches out old dirt and grime. We had to treat the entire area to end up with a uniformly clean surface.
Something else that we found that works on fabric and carpet (but takes a good deal of time) is what piratical sailor (https://www.practical-sailor.com/boat-maintenance/fighting-mildew-mold-and-lichen
calls formula b:
2 tablespoons of baking soda
2 tablespoons of borax
1 tablespoon of trisodiumphosphate (TSP)
Mix in 1 quart of warm water with stirring.
What worked for us on fabric and carpet is to spray the area with the formula b and let sit for a few days. Come back with vinegar and a brush. Repeat until the stains are completely gone, which could be 3 or 4 applications.
If you spent a good deal of time under those conditions, I suggest looking around the boat for other potentially impacted areas.
Cabinets, lockers, closets, under berths, etc. Any areas close to the hull is where there would have been excessive condensation and possibly a problem.
We just completed an extensive cleaning of the boat from stem to stern. Feel free to email me (paul dot stascavage at icloud dot com) if you find your problem is more extensive than you thought and I will share what I have learned.
All the best,
SM #466 - s/v Rita Kathryn
Exploring Brunswick, GA