Tamiya do a 'good' tinting spray, called Smoke grey.....I think its tc 31 or something.
Spraying lenses will pretty much always give a slight 'mistyness' which may be unwise for trooping but the results are pretty good if you are careful...
There are lense tinting spray for automotive lights, but Ive not seem them used like this to know iof they are 'clean' enough for lense use.
You can also mix the colour with clear laquer and spray very thinly which can work very well....