Targeting based on hate levels works!
When wearing a red coat I no longer target the red monster but the green one. When my color switches, it picks the appropriate target. This is for monsters based on how much each color hates each other color. You will target whoever you want provided they’re not your color. Monsters will pick a monster of whichever color they hate the most within their line of sight to attack.
Monsters can’t attack their own color and you need to be wearing the appropriate coat to get or use their color weapons and such.