Dogs then and now

the back legs are slightly shorter and the colorings have changed some

I thought the back legs only seem shorter because of its posture

Nope - due to breeding, their leg bones are actually shorter than they should be at the back, weaker than they should be at the front and more compact around the 'scruff' area. In relation to the legs, this means German Shepherds are renowned for their poor bone health - hip dysplasia and elbow dysplasia are highly common, debilitating illnesses for this breed. In addition, skin problems (such as allergies and pyoderma and calcinosis) are rampant among this breed, as well as a particular weakness to auto-immune diseases because inbreeding means they - basically - weaker to fend off attacks of this kind. Also, the deep-chested nature of these dogs - which human breeding specifically looks to focus on and emphasise - increases their heart conditions and heart attacks. In summation: human breeding is weakening and killing German Shepherds.