The "Red Coats" are roaming customer service agents in some Delta locations. It is really a coat. They do not fly on planes
The red uniforms are just one of the choices the flight attendants have - except in very large sizes (and caused a grievance with the NW AFA) . It is not a coat.
Since the theme now is semantics and insignificant minutiae, I feel compelled to note that they very well may fly on planes, just not in their red coats.