spraying clear colors

How big are the clear parts you need to paint?

I've never had a problem airbrushing clears (I airbrush a mix of Tamiya Clear Yellow/Orange to put the final touches on simulated varnished wood), but then I've never tried on a clear part. What thinner are you using? 

I've done a little.  Not with an airbrush, but by brush painting the backside of the clear part:

I used enamels, not thinned, because the "tint" on the colored lenses was supposed to me fairly opaque.

Depending on what you are trying to tint, (will it be seen from both sides of the part? how transparent the finished part needs to be?), this may work for you.

Paul

The parts are mostly about 1" square with one being twice that size (it's for Bronco's Buffalo 6X6). You'll be looking in from the outside although there's a door that will be open allowing you to also see the inside but only with great difficulty. The tint will be on the inside surface and isn't all that bad but it's not as perfect as I would have liked. I thinned with Tamiya thinner but not very much.

I have done small parts with a highlighter marker when the color needed was available in those markers.  It is too hard to make a uniform coating to do larger areas that way, however.