Over the years I've been at Kingswood Warren I've occasionally worked on projects that primarily benefit the BBC archives' restoration work, the most successful of these being the transform PAL decoder. A while ago I was introduced to another possible restoration job - recovering colour from black & white film recordings. This is all explained in some detail on the working group's wiki, but the general idea is that black & white film recordings sometimes captured the PAL colour sub-carrier patterning (when someone had forgotten to filter it out) and it might be possible to recover this colour.
My first, and second, thoughts were that this was a forlorn hope. You'd have to realign the film image with its original TV scan lines to stand a chance, and this just didn't seem possible. I'm glad to report that I've been proved quite wrong, as you can read in this thread on the Doctor Who restoration team technical forum.