Does a hazard warning button need to be red?

Seems like just about every car I've driven has a red triangle button or a grey button with red text/icon. However, I've seen buttons on eBay for other compatible VAG vehicles that seem to be neither red nor have a red triangle icon (they are all grey) - I'm assuming I can change to a grey one without affecting MOT etc? Can't find any regs that say it should be a certain colour... Would be nice to make the dash a bit quieter on the eyes!