Which is why I think designating gold/green/avocado (and later red) as the Command Division color was dumb as is having a Command division. As you said, we see all sorts in the Command color. From the CO down to the lowliest tech. And we also see reds and blues in the chain of command on ships and bases. So a “Command” color is a pit of a misnomer.
Agreed 100%. The "command division" seems to have little or nothing to do with who can actually take command. I've said many times that "control division" might have caused less confusion.
Where does that come from? BTS info? TMoST? Frank Joseph? FASA?
TMoST is the earliest public source, I'm pretty sure.
Are command level officers in their own division?
On a ship, there are really only two people who are not part of a department. The CO is on a higher plane, above such mundane things as departments. The XO is over all departments and works especially closely with the Admin department.
Most IRL militaries would to an extent disagree with you as they place both the security team and the people who shoot the weapons (though not always maintain them) in the same Department. Where they agree (as do I) is that the same individual shouldn't be doing both roles at the same time... rather the Weapons Officer should be on the bridge and concentrating on external defence and the Security Chief should be below decks co-ordinating the internal defence, with the Bridge Communications Officer acting as relay to the command staff.
Two or maybe three separate and mostly unrelated things there. Weapons control is highly technical and centralized, lots of sophisticated equipment and systems. Internal security is mostly disciplinary and policing, running the brig, guarding a few sensitive spaces and sentry watch in port, and as far as I know has always been quite separate from weapons and fire control in any navy. In the USN MA rates do that job, though other rates or non-rated personnel are often detailed for the more routine guard-duty aspects.
The third thing, that is often shown done by security personnel is ship's landing force. Traditionally in the USN landing force personnel were drawn from all departments based on a ship-wide assignment bill (roster).
Well, that's funny cos the command qualification is frequently held by most Chief Engineers in the US Navy and is mandatory for all "Command Officers" on submarines as part of their career progression and yet they very much have both Engineering Departments, Deck Departments and some even have Executive Departments.
I'm not sure most chief engineers have completed command leadership training or such, if that's what you are referring to. But they are unrestricted line officers, and as such potential executive or commanding officers. All department heads on a USN ship are line officers except for supply and medical.
Around the turn of the 20th century, the USN decided that line officers needed to understand engineering and propulsion since that's what moved their ships into action, and the separate Engineer Corps was absorbed into the line. The Royal Navy tried the same thing a few years later but switched back after WW1 to Engineering being a non-ship-command career. There are pros and cons of both systems and people on both sides who propose changing to the other system, but in general both have worked well.
Perhaps interesting: If engineering had remained a separate corps in the USN, we would have had different people as the first carrier admiral (Joseph M. Reeves), WW2 Vice CNO (Frederick Horne), and the highest ranking WW2 Admiral (William D. Leahy). All started in engineering at the Naval Academy.