Haha, this has me thinking now! xD Well, I may not be correct on this, but seeing that the Official Artwork
of Cloud shows it as 'dark blue' I'm gonna have to say that is outfit is officially dark blue. :P Pic: http://images1.wikia.nocookie.net/__...d-FFVIIArt.png
Also in the official Dissidia Final Fantasy artwork, shows it as a very dark blue...
But your fiancÚ is correct on his outfit being purple too. Though the Dissidia artwork shows it being dark blue, in game, it looks dark purple! O_O (To me)
Even the new game that is coming out called 'Theatrhythm Final Fantasy' decided to show Clouds outfit clearly as purple as well lol.
...Sorry if I am making making you rip the hair out of your head right now... x'D
...I guess it honestly doesn't matter, you can base your cosplay outfit purely on the in-game FF VII and Dissidia (dark purple) or more on the artworks (dark blue)
There is a lot of artwork and screen shots of Cloud out there, and most of them shows his outfit looking dark blue though... Almost even black. I'll be cosplaying Cloud someday, and I'll probably have mine in dark blue. But if it makes you feel any better, I have seen this cosplay of Cloud being done in both colors.
Hahaha, I guess Cloud has two outfits throughout the game then, which he actually changes (EVERY BATTLE ENCOUNTER?!) - unlike most anime and video game characters who wear the same outfit 24/7 lol. xD