What does "command" mean? Kirk as commanding officer would wear the green/gold of "command", sure, but then why would anyone else? Sulu wears green/gold - what does helm have to do with "command"?
Helm specifically, nothing much, I'd imagine. Wearing red seems to indicate the person in question is a line officer
(or whatever the equivalent term might be in-universe).
As an explanation this creates problems when we consider that Data is second in line to command, though. But I guess you can only wear one color uniform and since he's Ops Officer under normal circumstances, I can overlook it. He wore red when serving as Riker's XO in 'Gambit'.