Yeah, most countries will not allow any light except for forward facing white lights (head lights) and amber for indicators. Even the light emission wavelengths, frequencies, PWM and lots of other things are regulated (as it should be). Typically, only larger commercial vehicles have additional amber positioning lights and special vehicles like ambulances and police have other colors.

However, if you can switch the additional light colors off while the vehicle is in operation it might be legal in some jurisdictions (most aftermarket lights these days come with bluetooth remote controls or even mobile apps).

Show cars need these lights to stand out or to represent the brand or manufacturer of aftermarket parts for shows and exhibitions (ie SEMA). Other than that, it is all about personal taste.