I did a google search for clonetroopers and found this on Wikipedia reguarding clonetroopers and their rank system. Is slightly different than posted earlier so here's the link to the article and I've copied and pasted the section on the ranks
https://en.wikipedia.org/wiki/Clone_trooper
Originally clone troopers were identified in rank by the color of their armor, as in this chart below. However, by Episode III: The Revenge of the Sith, colors became associated with a trooper's legion affiliation.
Black — Shadow Trooper
White — Clone Private (standard trooper)
Green — Clone Sergeant, commanded squads made up of 9 troops.
Red — Clone Lieutenant, commanded platoons made up of 4 squads (36 troops)
Blue — Clone Captain, commanded Companies made up of four platoons (144 troops).
Yellow/Orange — Clone Commander, commanded regiments made up of four battalions (2,304 troops). Many of these commanders were grown with more capacity for independent thought than their troops, and were sometimes known by names rather than numbers. They also received training from the ARC trooper Alpha-17.
Once the Galactic Empire is established, all armor uniforms of the clone-troopers, now re-classified as 'storm-troopers' and issued new armor, are once again all white, with no outward signs of neither rank, nor legion or other unit affiliation.