Advice on cleaning moulding

[Waterborn]

I was sanding my waterline stripe the other day to rapaint it. The sugerspoon transom on my Benny is a nice handhold while sanding the last few feet at the stern. When I was done I found that the moulding at the transom was covered with a green powder in many spots in the shape of my handprints. Wiping it with a rag, even with some cleaners only smeared the green deeper in the moulding strip. Does anyone have any ideas on what would take the colour out and return it to it's original white (ok, off white, It's not a new boat) finish? I am afraid I cannot say for sure what it is made of. Vinyl, plastic, poly-somethin',somethin.
Cheers!