Roger:
It was possible to keep first-generation smooth-tops pristinely white, but there was a catch - it was more work than keeping a conventional cooktop, with its burner bowls and possibly trim rings, clean.
You had to use the correct cleaners (the ones available then were Corning Smooth-Top Cleaner for regular cleaning and polishing, and Delete for tough stains), and you had to clean it properly after every use. Part of the trouble with white smooth-tops was that if you used a sponge or cloth that had been used for other kitchen cleaning, it was likely to have microscopic food particles in it. If you just wiped the top with one of these, it could look clean afterwards, but the next time you turned the range on, the food particles deposited when you wiped heated and darkened. Minerals in water could do the same thing.
They looked nice and space-agey, but they were actually more work; the easy-cleaning promises were basically bogus. The reason that smooth-tops are dark colors today is to avoid all this hassle.