In the UK you can have any colour anywhere as long as it is not a white facing backwards or a red facing forwards. Basically there are no laws saying you can't so you can!)
The Road Vehicle Licensing Regulations are quite stringent, not least to include uniformity (for example placement of lighting has to be equal on either side with the exception of fog and reversing lights....http://www.opsi.gov.uk/si/si1989/uksi_19891796_en_1.htm
These only cover vehicles that are on the public highway though, so at a show, etc. You can do as you please.
It get a bit more difficult with LEDS, but I checked with my local traffic unit, and basically clusters of LED's are categorised as being one light unit. Hope that helps