Blue Jackal
From Halopedia, the Halo wiki
"Blue Jackals" can only be seen on one level in Halo 2.
To see a Blue Jackal, you must play the level, Metropolis on any difficulty. Kill a Jackal on the Scarab. If it is on the right place, it will appear blue, as though it were inside the Scarab's tech innards. This is due to coloring error in ground establishment on the Scarab (a part of the Jackal is "inside" the Scarab, and anything labeled as "inside" assumes a blue tinge and dye). It may work with other varieties of Jackal on the same Scarab. Also, if you melee the body, it will change to other colors, strangely including yellow and red. Also, when you turn on your flashlight and point it at the Blue Jackal, it will turn to normal colors, but when you turn off your flashlight, it will revert to blue again.
This rarely happens to Elites & Grunts (mostly the Majors) -- Mechanical-Menace
