bug#50141: Current part of emacs red, other parts blue

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: 積丹尼 Dan Jacobson <jidanni@jidanni.org>,
>   50141@debbugs.gnu.org
> Date: Sat, 21 Aug 2021 14:48:01 +0200
> 
> However, Dan's request has come up a number of times (e.g., bug#12056,
> which I'm merging this with), so I'm wondering whether we should add
> something like this...  or at least add some infrastructure that would
> allow it.
> 
> The obvious thing would be to run something from `select-window', but I
> don't see any obvious hook that we could be using there.  Am I missing
> something?  I was thinking about adding a minor mode for changing
> background colours in windows...

buffer-list-update-hook sounds like that infrastructure.