No, the father doesn't have to be purebred. The moher and the father surely must carrie colorpoint, but non of them have to be purebred. Your cat probably do have some ancestors (at least one from them others side and one from the fathers side) that are Siamese, Birman, Ragdoll, Persian, Devon rex, Cornish Rex etc. but it doesn't have to be the father. It can be a grandmother and a great grandfather or so.