This was so very interesting. What an unexpected angle.
I think what many commenters don’t understand is that you are not asserting that “dogs are racist.” You are asserting that “human racism can affect dogs too,” which is a powerful point to make that I don’t think anyone has ever even considered before. Human racism is so powerful that it echoes to other members of the animal kingdom. I can totally see the logic in a dog copying its owners subtle yet racist reactions to people of another race. I hope someone does a scientific study of this.