When Doctor Who returned to BBC1 in January 1970, it looked and felt like a very diff erent show. With Jon Pertwee replacing Patrick Troughton as the series’ lead, with new opening titles, and with a near-future England becoming the exiled Doctor’s home, the only really familiar elements were the theme music, the TARDIS’ police-box exterior and the recently introduced UNIT organisation. Technically, however, the most significant change was that the programme was being recorded and transmitted in colour for the first time - although, ironically, the majority of households would still be watching in black and white for several years to come. But for the show’s designers, it was business as usual. As stills from so many 1960s productions prove, Doctor Who had always been made in colour; it just hadn’t been seen that way
Over the course of the decade, no fewer than 38 individual designers would work on 59 stories. Each brought inventive and creative solutions to an array of technical, production and budgetary challenges in the light of often restrictive BBC procedure and protocols, rising inflation and escalating industrial disputes
Of all the technological innovations that Doctor Who embraced in the 1970s, the one that had the most significant impact on its design was surely Colour Separation Overlay, or CSO for short. Via CSO, the output from one studio camera could be electronically keyed into that of another, using a single block colour (usually blue, yellow or green). This meant that actors could be placed against photographic backgrounds, model shots, or pictures from other cameras - saving time and money on set construction and dressing, as well as freeing up valuable studio space.