I posted a sighting that I had of one in October of 2010: http://lansingwbu.blogspot.com/2010/10/american-robin-with-white-feathers.html
Right now scientist describe two kinds of Leucistic birds, pale and pied. Pale leucistic birds will have the same markings, but are extremely pale. Pied Leucistic birds, like the one in your photos, have patches of white. Leucistic birds are relatively unusual but much more common than albino birds which are completely white with pink eyes, legs and bill.
The bird is perfectly healthy but they may have it harder due to their different coloring. Predators may find them easier and mates may not find them acceptable at all.
You can read more at: http://www.birds.cornell.edu/pfw/AboutBirdsandFeeding/Albinism_Leucism.htm
Thank you for the information. Maybe someone else can learn from this. Thanks! ~ Linda