Having extensively used cad plating on early American and British motorcycles i restored in the 70's and 80's, I remember cad having a flat finish, more "white" in appearance than the bright "silvery" sheen of zinc.
That i am aware of, zinc was first seen on Japanese motorcycles, not in use by other American and European motorcycle manufacturers prior to the 70's. (As an aside, H-D's, at least up to the mid-50's used a process called "Parkerizing" or phosphating.)
By the early to mid 80's, attention to exposure to cad toxicity and expenses meeting environmental regulations minimizing waste by-products took cad out of favor with industry. I remember this, because cad platers i was using began quitting using the process and i had increasing difficulty finding platers who still worked with cad.
I don't believe Honda used cad plating, at least on the 750. If cad plating was used by Honda, by my observation, cad may have been on spokes only, as the finish on original Honda spokes appears different (less shiny) than the finish on nuts, bolts, washers. Just an opinion, nothing i have a basis for, other than the plated coating of cad is not as thick as zinc, more oxidation resistant and has a quality of lubricity preferred in threaded assemblies.