[AdrienVeidt]

Personally, I say the various uniform and vehicles colorations are indicative of which COBRA General they're mercenarily working for. In my 'verse, there is no one COBRA Army; there's several of them usually working together under whoever happens to be leading the organization at the time. However, if one individual - such as OverLord, let's say - decides to fight against another - we'll say COBRA Commander here - then the armies split along the divisions of who's paying who.

Generally speaking, the smaller the unit or installation; the more likely all the Troopers work for one General. But as large installations such as TerrorDromes can't necessarily be funded by one General, he/she'll have to cajole other Generals into buying into whatever mad scheme he/she is cooking up and thus Troops from that other General's army are likely to be working there as well.

Rank is worked out a lot more similarly to how it's done in the Star Trek Mirror Universe, where your rank is basically whatever you've the balls and skill to take, moreso than what you earn.