Conditioning. The game has conditioned you since the beginning to see hostile AoEs as red/orange and friendly AoEs as blue (e.g. limit breaks). I'm not sayng you don't have a point OP, because I certainly see where you're coming from, but I can only assume the devs figured it would be more confusing for people to teach them that suddenly it's okay in the red. Well, that and you wouldn't have to worry about which your on because red ground thingy would always = bad, while blue ground thing would always = good.