Apparently, fans have been wondering why Noctis and the rest of his Final Fantasy XV crew are all dressed in black. They've taken to the official forums to voice their questions, and the game's director, Hajime Tabata, stepped in to address the issue.
According to him, the clothing is "official battle gear" of the Kingdom of Lucis. He goes on to explain, "Noctis is a member of the royal family and the other three characters are parts of various Lucian national organisations and they are each wearing the specific battle dress relevant to their individual stations. In the Kingdom of Lucis where our heroes reside, the color black has historically been treated as a special color. 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 coloring. 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. So watch out for that too!"
Uh, that was way more detailed than I expected. Tabata seems to really care about XV, and as I've mentioned in the past, I have a lot of hope for it.