The cannon fodder enemies of the Marathon series, equivalent to Halo's grunts, are the tall, long-limbed, three-eyed, color-coded, masked Pfhor fighters. One can easily imagine that the idea for Grunts started with the Pfhor fighters with their limb length and height drastically reduced, removing the third visible eye, and exchanging the long staff weapon with plasma pistols, needlers, and eventually fuel rod guns. As with Grunts and Elites in Halo, enemy ranks are indicated by colors, with the more rarely occurring colors indicating relative strength. Just as rarer gold Elites in Halo are stronger than their more common blue counterparts, so here one would expect the orange Pfhor fighter to be stronger than the green, which are fare more plentiful in the game's opening level (Waterloo Waterpark).

Bungie has tended to produce enemies with at least two variations, usually referred to as Major and Minor, with the stronger Major unit indicated by a rarer color. In addition, variations of armor and equipment are sometimes added to create additional variations. Images of most enemies in the Marathon series can be found at:

http://www.eyrie.org/~aerianne/marathon/

(Marathon 2 running on Aleph One with XBLA Marathon: Durandal textures)