Joe Compel has some good black back and brown back pics and info.
http://www.joecompelreptiles.com/collection/

Some people would call those black backs...some would not. I am one of those that would not call those black backs. But I do see alot of snakes similar to those being labeled as 'blackbacks' but that is just probably some marketing so that they can sell normals for a higher price. IMHO...without the trait being genetic, all they are is just nice looking normals. Prove it genetic and it is something great to incorporate into another project. Pastels with no pattern on the back are amazing.