When Archer examines the film he's been given, it is clearly modern colour film. Back then it would have been black and white, and if it were actually colour, it wouldn't have been possible to process it at home.
The main character opens a can of 35mm film and pulls some color negative strips --identifiable by the orange mask- containing photos of some documents. Color negative film was unavailable until the 50's and even then, a spy would have used much faster B&W stock.