Rtas 'Vadum's eyes glitch
From Halopedia, the Halo wiki
In the level Oracle, the part where you just start and Half Jaw and the other SpecOps Elites turn invisible, look at Half Jaw eyes. Though he's invisible his eyes are still green and stand out from his Active Camo. This does not effect him in any other way than just making a player laugh. This doesn't work with any other Elite known.