As a side note, I'm working my way through Voyager season 3 and there almost always seems to be a red-shirted command officer at Mission Ops. Not sure what that really means, unless a red-shirted Tactical officer is manning it, or a relief bridge officer instead of an Ops officer.
I know this topic is nearly dead, but I'm still churning through Voyager and an episode shed some light. There's an episode late in the 5th season where 7of9 is considering crewman to go on her first date with. The first is a red/command-shirted officer who is "assigned to the airponics bay" which would lead me to believe he's a command character who remains in red even though he is assigned to manage a science dept.
I've also been paying attention to crowd scenes on Voyager and there are a ton of red-shirts represented. In the average shot of 8 random crewmen 4 will be ops, 3 command, and only 1 science. I know that the production side of things is probably more worried about which costume off the rack fits which extra more than they are worried about in-world sensibility, but I thought it was noteworthy.
One thing to keep in mind is that Airponics is not a standard duty post. It was converted out of a Cargo Bay in order to reduce demand on the Replicator sysem. Also remember that Voyager had suffered casualties and crew were being cross-trained like crazy. I would not assume that the red shirt's primary duty station was Airponics.
Also remember that originally Voyager had been on a specific anti-Maquis mission and probably had a reduced Sciences section, while Command would have been at full strength and Security/Tactical would have been beefed up. This may also have been why they carried a tricobalt device in addition to their standard arms loadout.
I figured that someone would point out the nature of the mission (understaffed, chasing the Maquis) as a disqualifying factor. That's totally reasonable, but it would still stand to reason that a command officer assigned to science might still remain in red.
Of course he or she would. Officially they're still in Command branch TDY to Sciences. However, going back to the original conversation Command branch handles a lot of stuff that one doesn't really think about that is required to run Starfleet every day. Where Tactical Officers are in Operations branch, they are merely the weapons officers. Tactics and Strategy are handled by Command personnel as are staffing, discipline and most other administrative duties. Look at it this was. Operations branch has a lot of personnel simply referred to as Operations. They do a lot of the nonspecific duties in Operations that aren't specifically handled by Engineering, Security/Tactical or what-have-you. Same thing with Command.