What ever you call it, adding color to old photographs, whether Black & White, sepia toned, or some other half-toned process, is sure to raise howls of protest from purists. The debate will never end, but I don't see the problem in playing with a copy as long as the original is unharmed. Even photographs of great historical significance.
This picture of Mata Hari, from 1910, prompted such a
discussion bitch fest. I like it in full color. The color brings out the detail, makes it more lush, and of course it's boner better.