Here's a quick guide to tinting light with a spray can type tint. It costs about $30 NZD for a can but that would do at least 4 sets of lights. Also it is illegal to have any alterations like this on lights in my country and although I haven't had any trouble as of yet, be careful.

Step 1: Remove Lights

For my car I just had to pop the boot and there were two screws underneath it for each tail light. Undo the screws and the light slides out a small way. Reach in behind and undo all the bulbs, They were a stiff quarter turn anti clockwise to undo. Remember where each bulb went so you can put them back correctly!

Step 2: Mask Up Lights

Use masking tape that isn't to sticky so as to leave residue on the lights and cover up all the parts you don't want tinted.

Step 3: Paint Them

Put them somewhere that doesn't matter if it gets oversprayed. Follow the directions on the can for flash off time between coats. Paint until darkened to your liking.