I bought some spray canopy tint from the LHS and gave that a shot. First try came out WAAAYYYYY to dark with ONE very light coat! DAMN I thought I was up a creek! Used some nail polish remover, and painstakingly removed all of it... (took nearly an hour to get it all)
Figured I'd give it one more shot! first coat, was sooo light I could hardly see it! I ended up doing 3 coats for a nice even tint.. I guess the nail polish on the plastic did something to make it not absorb so much of the tint, anyhow it turned out great, soft even coats, very easy to go back and correct a light area cause it doesn't absorb much.
Of course TEST the nail polish on a scrap piece first!

Good luck
~Andrew