It's game design, not psychology (Score 1)

Like most games, Unreal Tournament uses more warm lighting than cool, making cooler colors like blue stand out better against the environment. If it's easier to see, it's easier to hit, and in Deathmatch, hitting is all there is to the game. Also, half the guns in Unreal Tournament 2004 shoot projectiles that explode, with most of the explosions being some shade of red. More red things dynamically moving around the environment makes it harder to track Red players.

Perhaps the researchers should apply basic logic and play the game before leaping to conclusions.