The episode was originally recorded in colour. However, in the Sixties and Seventies the BBC would sometimes wipe and re-use the master tapes once the programme had been aired. Film copies of the master tapes were often made of programmes prior to being wiped, but the recordings were only made in black and white. Thanks to the development of new Colour Recovery technology, the preservation team within BBC Archive have been able to bring a new lease of life to specific archive content, and this Dad's Army episode is the first programme to have its colour recovered. Colour Recovery relies on the particular manner in which these film recordings were made, and hails from the Colour Recovery Working Group, an independent group which has been working on the development the technology – the idea for which was conceived over a decade ago. (thetvdb.com)