When I got my grills painted black, the body shop was painting a set of lights for a different customer. They have a clear paint which can be mixed with any color to give that tinted look. He said it works perfectly on plastic, won't chip or peel off like tint film used on windows. He also said they have this paint for wheels if you want that charcoal polished/gun metal look instead of chrome or silver. I think I may get my lights done!
I certainly wouldn't use the film and wouldn't recommend it either.
If you want to do it the cheap way, you can buy tint spray paint and do it yourself. I think I've seen it on ebay...