User blog comment:B214/Volume 22 spoilers/@comment-3965848-20161204121455/@comment-30048084-20161205180035

@Striker10 the top they are wearing is called double breasted I can't give you a particular style of their jackets though just that they are double breasted.

The problem in Bova's case is that the anime shows Tannin as bipedal while the light novel does not actually specify if Tannin is bipedal as far as I know so I doubt whether Bova is wearing any armour or clothing.

I think we can assume that all of Issei's peerage wear

Crimson coloured(stated)

Double breasted jackets with white ties

some form of a cape that is purple

everything else is suited to the individuals combat style or preferences.

an original name: Blazing Truth