mode-line-buffer-id-inactive face doesn't seem to work

[muirdm]

I'm trying to darken the buffer id when the window isn't active by setting mode-line-buffer-id-inactive, but it doesn't seem to have any effect. I tried on emacs 25 and 27.

To test, I started emacs -Q -L <path/to/powerline> version GNU Emacs 25.3.1 (x86_64-apple-darwin13.4.0, NS appkit-1265.21 Version 10.9.5 (Build 13F1911)) of 2017-09-13 and ran something like this:

(require 'powerline)
(powerline-default-theme)
(set-face-attribute 'mode-line-buffer-id nil :foreground "blue")
(set-face-attribute 'mode-line-buffer-id-inactive nil :foreground "red")

And saw this (both buffer ids are blue):

Am I doing something wrong?

[c-alpha]

I think you should be using/customising the faces powerline-active0 and/or powerline-inactive0 instead.

(NOTE: It seems that mode-line-buffer-id-inactive could be a candidate for being marked as obsolete. But as I'm not the maintainer, that's my very personal point of view only. END NOTE)