There's a post a few months back about how to tell the difference between motley/striped vs striped corns. Since the striped pattern makes my eyes hurt, I didn't pay attention to the details, but it has something to do with the relative widths of the stripes.
Genetically, the striped corns are homozygous for stripe, the motleys are homozygous for motley, and the "motley/striped" are the ones which are heterozygous for both (which contrary to the 'common' meaning of het, gives a non-normal appearance.)
If you're getting motleys, motley/striped, and striped offspring from the same pairing, then both parents are motley/striped corns. :)