The whole story? Exceptionally, Memory Alpha has it more or less correctly:
http://memory-alpha.org/en/wiki/Kathryn_Janeway
Apparently, Janeway started out as a junior Science Officer, much like Spock (and much like Saavik, who also wore Sciences grey in ST3 after attending what looked like Command School in ST2).
The little episode about her "first command" apparently didn't deal with command of a starship, but rather with a short-duration command of a specific mission - perhaps an away team or somesuch. She probably held a rank of Lieutenant or lower at that point, so that Tuvok could dress her down.
The bit about her being a Commander in charge of away teams aboard the
Billings might indicate she had made XO, but the SO might also have that sort of responsibility. Nothing in her backstory would absolutely require one or the other.
It is implied that the
Voyager was her first starship command, but AFAIK never made explicit. It also seems that the promotion to command was more or less simultaneous with the promotion to Captain rank. We just don't have the details. It's quite possible Janeway already wore red from her
Billings posting, but it's equally possible she wore blue - or perhaps mirrored Spock and sat on two chairs, wearing one or the other of the colors.
Timo Saloniemi