I've had success with two methods. First is to dip the clear plastic part, attached to a small piece of the sprue as a handle, into Future tinted with food dye of a suitable colour. Repeat as often as you need, at hourly intervals, then leave to dry and cure under a cover (to prevent dust) for at least 2, better 3, days. Simple and it works, but be careful to wick off excess Future with a cotton bud, and watch out for drips and runs starting to form.
The canopy on this Hobbyboss 1/72 TA-7C was tinted using this method:
Alternatively, Use Tamiya clear acrylic paint of the colour you need, heavily thinned, and sprayed at low (less than 10psi) pressure. Use repeated coats to build up the degree of tint you need, and ensure that the previous coat is dry before spraying the next one. Resist the temptation to work too quickly, or the chances of the paint running and spoiling your work will be excellent. It can often take ten coats or more to build up a sufficient degree of time, and I must re-emphasise - don't rush it.
The canopy on this Revell Germany 1/32 ASK-21 glider:
and the pods on this 'what-if' VVIP Harrier:
were done using this method. Sorry to use aircraft to illustrate, but I don't do cars very much:
Whichever method you use, remember to apply tint from the inside. That way, you can't damage it accidentally while painting the rest of the model.
Cheers,
Chris.
Cute and cuddly, boys, cute and cuddly!