just leave it out in the sun a couple of days!
a friend of mine brought her boyfriend andhis new navy blue boardshorts with her one day. His shorts left nice blue stains all over our white vinyl!
after a few weeks (2 days of sun each week, we are only out on weekends) it wasn't even noticable, after a couple more you couldn't even tell it was ever there when looking for it!
Just leave it bake!