When it’s done for commercial purposes I’m totally, absolutely, 100% against colorizing anything that was originally filmed in black and white. Something like Citizen Kane is an excellent film without color and colorizing it would just be horrible. Even Ted Turner learned that lesson and gave us something nice by way of apology.
That said, I can appreciate someone doing it as a technical experiment. And so, that in mind, here’s someone’s efforts at colorizing the final conversation between the First Doctor and Susan from “The Dalek Invasion of Earth“.