With the ability to use your multiplayer skins in the single player, a small oversight has appeared in Halo: CE Anniversary Edition.
You see, the skins were initially meant only for CEs’ multiplayer, which only exists in a Classic form. As such, the skins don’t have a Remastered equivalent. This means that while you CAN use your multiplayer skins in campaign, in order to see them you have to stick to Classic visuals mode.
A small update that adds in Remastered equivalents to the existing skins would help, though I don’t know how feasible this is in-game.