There's nothing hugely special about Anti's uniform, it's just a set of fairly durable and somewhat stylish clothes, worn over his bodysuit and some components of his armour. Typically uniforms like this are only worn during more formal events, or sometimes during non-combat duty. Unless combat comes almost ouf of nowhere, the crew would switch to full pressure suits (typically armoured). To avoid explosive decompression Imperial ships vent all atmosphere during combat. It also serves to insulate the crew if the heat really starts to build up, buying them a few more minutes via eliminating convection and part of conduction so they won't cook quite so fast and can more easily retreat or abandon ship.

Art is by  Fetalstar

Antinov and Avalonians are both mine.