replacement for whitespace-tab

[Will Parsons <wbp@nodomain.invalid>]

I noticed that in one of my Emacs configurations I had customized the value
of whitespace-tab to better distinguish visually tabs from spaces.  When I
did a C-h v on the variable (under Emacs 25.2) I got the message:

  This variable is obsolete since 24.4;
  use the face instead.

Unfortunately, this extremely terse message gives me no useful information on
how to actually *replace* whitespace-tab.  I have looked under the
customization buffer under Faces and see no obvious candidates for
highlighting tabs, looked under Emacs News in vain, and searched the web
(which frustratingly tends to yield a lot of obsolete information).  So what
*is* the officially approved way nowadays of highlighting tabs?

-- 
Will