Funny you should mention the white mouse, Tim:
There was a Playmo exhibition in Mechelen (Belgium) in the toy museum a few years ago. Didn't see anything quite as impressive as we can see here, but there was one thing I really liked: a machine spitting out white mice!
Just to show how it is done, I guess. The pile of mice was just there for the visitors: you were allowed to take some home (I guess mostly children were interested)

I have no idea which animals are rarest. Colour animals
that are still white would be my best guess too, since they're old and a lot of those sets got painted on. I have (badly) a painted dog and a few painted horses
