Red Armor are enemies form Kingdom Hearts (game) in various tourniments, but fighting one outside Olympus Coliseum is exclusive to Kingdom Hearts: Final Mix.
Red Armor are red variants of Guard Armor that replaced the Guard Armor that appeared in the Olympus Coliseum in Kingdom Hearts. Therefore, red variants also replaced the Hammerlegs, Gauntlet, and Armored Torso enemies. Red Armor also seem somewhat more feminin than normal Guard Armor, as it's color could be mistaken for pink. It also has a larger collar and moves in a slightly more faminin way.
A Red Armored Torso was the boss of the Phil Cup.
Red Armor made full appearance in the Hades Cup under the name of Guard Armor instead of using the names for each individual part.
Red Armor and Guard Armor have the same attacks, but when you are fighting a Red Armor, it seems easier then fighting a full Guard Armor, because more than likely you will be a lot stronger.