In North America, dyeing dogs is illegal in Colorado, Florida, Maine, and South Carolina. These states have laws against the practice, often under animal cruelty or mistreatment sections of the law.

Here's a more detailed breakdown:

Colorado: Specifically prohibits dyeing animals for show or sale. A dog can be forcibly removed from an owner who has dyed the animal's hair, and a minimum $1,000 fine is imposed.
Florida: Has laws that make dyeing your dog and other animals illegal.
Maine: Has specific laws against dyeing animals for show or sale.
South Carolina: Has laws that prohibit coloring or dying animals.
Other animals: These same statutes often protect baby chicks, ducklings, rabbits, and other animals.

In Canada, there are no federal or provincial laws that specifically prohibit dyeing a dog's hair.