Very well! I am doing just that in the revised patch. So there should
be no visual difference between this and the prior state, except for one
case: the empty Git stash header, which will ultimately inherit from
'shadow' (before there was a "FIXME" to disambiguate it from other
header values).
Looks good to me; pushed to Emacs 28 now.
I don't know if anyone else has such problem, but now highlighting
the empty Git stash header with a different color distinguishes it
from other header lines, and thus attracts more attention.
So now the most noticeable thing in the vc-dir is the Git stash header
(that I almost never use).