The Greenberg guide to Marx trains, Vol 1 (prewar), page 44, has 2 photos of Bunny locos - one with blue eyes and one with red. Actually, it's a little wierd, the bunny with the blue eye has a blue iris with the black pupil in the center - like a normal eye. The bunny with the red eye looks like it has a clear or white iris with a red center pupil, which is , ummm... different.
But, as Steve says, looks like both are original.