There are obvious cases where the film will grate with we experts but as orca said, he couldn't recognise light blue errors nor could we recognise dark blue or green ones.
There are other cases where we are absolutely certain that the film is wrong only to discover from contemporary sources that they were right all along. RAF headdress is a case in point - officers wearing berets with flying suits and forage caps with No 1s, or SD hats and DPMs. Another was Busy Jackets with shorts and long or short sleeves.