Plenty of water, magic erasers, and Westley's Bleche White.
Spray Bleche white small area work with magic eraser and hose off. move to next area...repeat.... Wear a white t-shirt...
oh, and there is the other way..... see what I did to a boot cover:
Using magic erasers, a soft closed cell foam scrubby and my cleaner, it was clean but now still grey.
So I said looks like re-dying time.
I don't give a dam usually about being green, but this time it paid off:
gray/white side by side
What made this transformation?
Taking the boot off the car and place it where you can lay it flat.
Use the Green Can of Brake-Klean ( the environmental friendly can). The other stuff is tooooooooooo extreme.
Spray an area about 12 inches by 12, and get it wet let it sit about a good 5 count and then using a good non-colored rag rub like hell. Re-spray and flip the rag to a clean side.
It will pull all the dirt and crap off the vinyl, and evaporate without ruining the vinyl.
When finished use the protectorant of your choice mine is 303 aerospace.
You have to use a bunch It took 3 1/2 cans and about 12 good white rags but it worked and I don't have to re-dye the thing.
Let it air out.....