Fleet Flavor and Unit Identity
It was always a Union policy to foster friendly rivalry between dorm groups, ships, fleets and branches of the military. This constant competition is seen as a way to keep morale up, hone the readiness to compete and the will to win.
Since combat and war are the ultimate competition where only winning counts, this mildly encourages and usually not forbids it.  This is the reason behind inter-service sporting events, group and unit decorations.
Union Military exists now for almost 2500 standard years.
It is a long time for carbon based beings. Virtually all branches and all units have developed their own traditions, symbols, colors and ways of doing certain things.
This holds true for every Midshipman team graduating all the way to Army, Marines, Space Force and of course the Union Navy.
Traditions are not made, they develop and no one can really predict what becomes a tradition and what is forgotten.
While the standard Union Fleet Uniform is black, officers are allowed to add one or two things representing their society or religion or something similar. Units sometimes add things to the Uniforms.
But it doesn't end there, the members of the 4th (and several other fleets) live a codified life style and have additional unit regulations.
 For officers that enter command school, there is an interesting book, called the Twenty Five Thousand Unwritten Rules of the Union Fleet, and then some." - Union Press -4940(OTT)- 534th edition -5050