Now, given how over the top other Clan ceremonial uniforms are, the only real difference I can find between Clan Nova Cat and the others is that the Nova Cat ceremonial uniform shows more skin--but the Clans surely wouldn't care about that, right? Is it that it resembles casual clothes? Actually, this has piqued my interest. Why, of IIRC all the Clans, did Nova Cat feel the need to amend their ceremonial uniform for inter-Clan relations?
This is a great question and this passage has been rolling around in my head since I re-read it yesterday. I think you are right, I don't think it's about the skin. I think it's about the lack of formality and what that represents. Most of the Clans seem incredibly uptight and formal. Deviating from this is dangerous and potentially un-Clan like. The bonfire ceremonies that the Cats have are wild, untamed, and tap into something that is barely controlled/controllable. Worse, that Khan Rosse had a vision of leading the Nova Cats to a perfect society that was
not the one designed by Nicolas, borders on heresy.
Nicolas barely tolerated our quasi-mystical/"religious" attitudes, to eschew Clan formality at the Grand Council would be a slap in the Great Founder's face. I think the full-body black leather cat suit for the Kurultai is a concession and a protection that yes, we can come to heel, and not about modesty.