Yellow in Phase 1 armor denoted Commander rank.
However, that was when the army was brand new and hadn't finished expanding. Phase 1 armor didn't fit right and was modified and eventually phased out entirely. The clearly marked rank made officers easy targets, and replacement armor was usually delivered unpainted.
As a result, within a year of the war's outbreak there was no consistent pattern to armor decoration. Officers during the animated series tended to wear mantles and hakimas (the japanese word for a skirt worn as battle attire), and helmet visors of various designs appeared as well.
Basically, the clone army in ATotC was inexperienced and their armor paint scheme reflected what the cloners of Kamino thought would be a useful rank designation pattern. As with all pre-war armies, things that look good on paper tend to look less good on the battlefield.
That, and as time passed the clones became slightly more individualistic; they may have been cut from the same material but their experiences after leaving Kamino shaped them.
I suppose you could relate it to France's army before and after the Great War.