This is something I have done in the past on other cars, the filters are there obviously to colour the light, you can remove the filters by gently drilling off thier attachment points, then as you say use coloured bulbs, or just use clear bulbs painted with JARROLDS GLASS PAINT, about £4 a tin, and works ace but do need to let it dry for 24 hours as bottle says.
This way you can get all manner of colours and have a play about.
tabetha