Or perhaps Starfleet Intelligence, another branch that was first mentioned around that time, both in TNG and DS9. We never saw an officer who would have been explicitly said to be part of Starfleet Intelligence, other than the redshirt Admiral Pressman who was said to work for Starfleet Intelligence in "The Pegasus", so the color of that organization might just as well be yellow.
And it's entirely possible that the other two yellowshirt branches mentioned, Engineering and Security, are also headed by yellowcoat flag officers. Since no such admirals were ever shown on screen, their shirt color could not be established one way or the other.
But in show production terms, yes, this was a unique appearance, and it's a bit curious why the costume made no further forays to our screens...
For related trivia, let's remember that flag officers in TOS were seen wearing both gold and red to roughly equal degree. Let's also remember that early TNG after the first season had some one-off or two-off "nonstandard" flag uniforms until they settled on the model that persisted till ST:FC; perhaps this reflects the great degree of freedom that the high brass has in customizing its personal wear?
Timo Saloniemi