I think they are holdouts from the clone troopers and mean the same thing they do for clones. This is why not all sandtroopers had them (which in reality is just that they were background and the prop dept. didn't care as much about them), e.g. they were ARC trained.
Being ARC troopers makes a whole lot of sense - I'm sure the Empire would still have some. I mean, for a long time the pauldron signified something - it wouldn't all of a sudden change to be rank, when having rank externally displayed was totally unnecessary with stormtroopers, and also later clone troopers (e.g. EPII clones color was rank, but this was no longer the case by EPIII.
This is why I take issue with the TK Commander being designated as such - what in the world would possess them to adopt an identical funky color scheme. They should have designated the TK Commander something else, such as a particular unit designation just like in EPIII the clones are identical except for paint scheme.
Sometimes I wonder what the dudes writing for LFL or creating the toys are thinking - no logic behind the dross explanations at all, and much of the fan ones make so much more sense.