Director Sir David Lean insisted on using three-strip Technicolor film despite it being difficult and costly to obtain in wartime Britain. In doing so, he was obligated to have a Technicolor consultant on the set to ensure everything was photographed correctly to Technicolor's standards. Lean was annoyed by their interference and mainly ignored them, hence this film does not have the look typical of a Technicolor film from that era.
The comment early in the movie about buttering the cat's paws comes from a technique used when a cat is moved to a new house, that is, if a cat has butter on its paws it will stop to lick it off and, as cats are very clean creatures, the butter and bits of dirt/dust/debris on its paws will inevitably annoy the cat, causing it to sit down to clean itself, thereby taking in its new surroundings, creating a mental map of where its new home is, and helping it to make the adjustment to its new surroundings.
Director David Lean offered Robert Donat the role of Frank Gibbons, but he turned it down because he objected to the character's political statements. Robert Newton was given the role, but with a contractual stipulation that he be fined £500 each time his drinking delayed production. By the end of filming he had used up his entire £9,000 salary. However, the producers overlooked this matter and paid his full fee.