if you open up your pet and go to collar color and select one, you get the wrong color. I think the wool positions need to be fixed. For example when I select white I get black collar and the other way around. No texture pack and the items id's tell me that I'm not being stupid xP idk about sheep, might be different
I remember a bug report about /pet dog collars from many months ago, I am not sure whether it was fixed back then, I would need more time to search the thread.