I'd tweak that slightly to maybe say that command is the standard track, with engineers, medics and other specialists admitted by slightly different routes (though why security and engineering share a colour baffles me, unless the main job of security is cybersecurity, with packing a phaser bottom of the job list? Anyway). But anyway, yep, command as the non-specialist start, with people from the other colours sometimes going across as they get promoted. And command officers specialising as they realise their forte.