What is so distinguishable about the different Axanthic lines. I have seen plenty of baby Axanthics that you could not tell apart if you weren't told what line they were.
As for Sulfurs and Fires, I do find them different at birth. From what I have seen, Sulfurs start out a bit more drab and get lighter with age. The Fires start out pretty bright or light colored, and tend to retain their color as they age. As for the Supers, no there is not much difference, but the difference between a Super Lesser and a Mojave Lesser Leucy is almost unnoticeable, and sometime completely undistinguishable.