of course you can!!! (dye them that is) i dyed my two white pet rats to be able to tell them apart. i used koolaids, one cherry and one grape, it worked better on their tail than their coat but it made for neat pics if yuo want it to last i suggest using permenant markers, it doenst hurt them at all. The breeders use permenant markers on the base of their tails and if the actual pet rat breeders use it, its fine.. ive never heard of any adverse effects of doing either method i suggested