Following on from the colourisation of black and white images and clips, which we looked at here, there's the Doctor Who Restoration Team's project to restore colour to three Pertwee stories which only survived in the Beeb's archive as black and white episodes - The Daemons, Terror of the Autons and The Silurians. These were colourised using home recordings of the colour shows, which had been made in the States, before the colour masters were junked.
Read about it here. It's one of those annoying websites where you can only link to the main index page, so you'll have to select 'VHS Releases' and 'Colour Restoration' from the menus. There's a wealth of info on the restoration work undertaken for video and DVD releases, and it's a shame I can't link you directly them, but browse for interesting bits on the restoration of the Ice Warriors and the Invasion amongst others. [I've found a link direct to the info here, although you'll need the other link if you want to browse their site.]
Two episodes of the The Ambassadors of Death were colourised before problems with the colour recordings haulted the project. Perhaps technological advances will solve this problem.
Colour recordings are missing for `The Mind of Evil', `Planet of the Daleks' episode 3 and `Invasion of the Dinosaurs' episode 1, meaning that frame by frame colourisation is required. The video releases used the surviving black and white episodes.