Yes, these dogs don’t need to have “rainbow fur”, but at the other hand (i don’t support that btw), does it hurt them? If the color doesn’t irritate their skin and don’t bring problems with other dogs cause of irritation (i would be interested in studies about that), i don’t see an issue with it, except its stupid. If the only thing resulting of it is the dog looks stupid (which the dog doesn’t care about) and the human with it is happy about it, the dog will enjoy the happiness.