I got pulled over for having blue fog lights, and I've had a buddy get in trouble for having red. Also, I know of someone that had purple underglow that's got in trouble because it was a mix of blue and red. When I got pulled over I asked the cop what colors weren't allowed, and he said all emergency colors. He listed the following as "not allowed":
Red, blue (for obvious reasons) and orange because of construction vehicles. Some cops are different from others, but I feel that is as strict as it'll ever get because imo, that's ridiculous. But just a heads up because some cops might not be having a good day