I too have heard that food coloring is safe. I know a person with a solid white long haired Chi. This dogs name is Pinky. So....the owner commonly dyes Pinky "pink". Pretty silly really but this dog sure does get attention. LOL
I would think as long as the dye cannot harm the coat or skin in anyway or hurt their eyes it might be ok maybe for Halloween or a special situation.
Oh and another thing. Please if any members of YT decide to dye their fur babies, Id like to see some pictures.