Bling of War: Except for the brief chunk of time that matched our Industrial Age, played mostly straight by the Imperial Legions. Beforehand, for much the same regions as Napoleonic (and previous) armies were quite dressy – well, that, and the giant steam clanks stomping around on the battlefield – and afterwards because big stompy Powered Armor with both noise and the ensuring thermal and neutrino emissions tends to make stealth something that happens to other people anyway, so you might as well go back to looking gorgeous on the battlefield if you’re anything other than scouts or special ops (who sneakily enough do have their own “field drab” armor which somehow never shows up on parade). And, of course, so long as the bling of war is on top of the fully functional deadliness of war and doesn’t interfere with its functionality.
This is, of course, completely unnecessary and not done by most people who advance past Industrial Age warfare – it’s just a local aesthetic preference. (The trope – which is still generally true in their universe – that the side with the shiniest uniforms tends to lose therefore has at least one qualification to it. That some people haven’t heard of said qualification and will fall right into the wrong assumptions isn’t strictly intended by the Admiralty, but they certainly don’t mind that it happens.)