My Ridgeback has lighter-colored areas over his shoulders – is that normal?

Yes. Many, if not most, Ridgebacks have lighter shading behind their shoulders, as well as on their necks and on their “britches” (the area you see from the “rear view”). Many new owners are taken aback at what they think is “weird” coloring, but it is entirely normal and visible on most every Ridgeback you will meet. You just never noticed.