SurLast or Sunbrella are "Solution Dyed" fabrics and cannot bleed or Sublimate onto any surface.
The staining issue lies within the vinyl characteristics.
Glues and foam backings cross contaminate the vinyl surface setting the conditions for staining to occur.
Additionally the staining can also be mold growth in the foam section that bleeds to the vinyl surface from the backside
Due to the expense many times the foam backing is not treated with antimicrobials.
Lack of a high quality top coat adds to the poor resistance of vinyl reacting to organic compounds that come in contact with it.
If it goes away when exposed to sunlight the condition is Dehydrochlorination.
Certain boat brands exhibit this staining problem while many others do not.
Higher quality vinyl’s resist any staining or discoloration.
Heat may be a contributor so if you're in a hot part of the country buying a Light Gray cover may help.
Not to brag but our SurLast BW+ Mooring Cover with the VacUHold trailering system is the best cover on the market and sold through OEM dealers.
Presently we supply MasterCraft, Malibu, Correct Craft, Centurion, MB Sport, Sanger, Supreme.
Check the videos of towed covers.