The Canadian DSO had nothing to do with it.
A Blue convertible top color option was indeed offered in 1964 1/2 Production, but I would not be surprised if it ran into early '65 Production as well. The big question is when that cut-off was.
Your car, VIN# 5F08C8xxxxx is a very, very Late '65 Production....so I heavily doubt that it ever came with a Blue Top since new. Chances are that the car never came originally with a Blue convertible top since it's such a late '65 build. It most likely had a White convertible top when new judging by your interior code color. I don't think that even Ford would have put a Black convertible top on a White with Blue interior. It just does not make sense. Stranger things have happened though..
(See Attached Pic) - Attached is a Factory 1964 1/2 Mustang Specs Chart. If you look at the Middle Box in the left column where it says "Convertible", You will see "Blue" listed as a convertible top color choice.
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Tony K.