The focus is the strap on this bag. Just sew strip of fabric down center of webbing to distinguish right from wrong side. Plus, it dresses it up really nicely. Full tutorial and pattern to make this messenger bag (aka satchel or shoulder bag).
How to make less bulky leather bag straps by backing them with fabric and only using two layers of vinyl/pleather. Looks SO pretty using a fabric to match the bag/lining and makes sewing much easier too.