That is the biggest question some fans are asking for a year after the game was revealed. The main characters for the latest chapter in the numerical line-up of the Final Fantasy series have the same color theme. Of course it makes them look like a modern-day boy band doing pop music for teens and doing world tour concerts, but the color theme behind it has an explanation.
At the Final Fantasy XV official forum, game director Hajime Tabata answered the question on why all four of the main characters wear in black, and here is his response.
The clothing worn by the four main characters is the official battle gear of the Kingdom of Lucis.
Noctis is a member of the royal family and the other three characters are parts of various Lucian national organizations and they are each wearing the specific battle dress relevant to their individual stations.
In the Kingdom of Lucis where our heroes reside, the colour black has historically been treated as a special colour. Because of this, the attire of the royal family and those in occupations closely tied to them are unified by having black as a base colouring. This part of the lore is the reason why the outfits of all four main characters are black. For the finished game we also intend on having their clothing having effects in battle and not just being a part of the world and its background.
And there you have it, but I am still guessing that fans will still make their own fan theory about the color these main characters are wearing, but then again, that is the beauty of having an active community for you game.
Final Fantasy XV will be available for the PlayStation 4 and Xbox One, no release date has been announced yet.