Thanks for the comments, guys.
Graham, Mike, indeed the Mustang would most likely have been dark green. The Luftwaffe's dark green colours were very often mistaken for black. To illustrate, I have a number of encounter reports from interceptions of Fw 200s and Bv 138s by FAA Wildcats (Martlets). FAA encounter reports have a field where the pilot can make comments on the enemy aircraft's camouflage and markings. Indeed many of them say their opponent had all-black camouflage.
Simon please post that link again! It wasn't terribly relevant, but it was very interesting nonetheless!
