Reporting this bug to the mailing list on request of the leuven theme
author as they believe the issue may be within Org and/or Emacs.  The bug
as reported to the theme author can be found here [1] and includes
screenshots to illustrate what I mean.

In short, the colors defined by the leuven theme for org-quote, and
org-example do not display as defined.  The screenshots will make it
clearer.
GNU Emacs 27.1 (build 1, i686-pc-linux-gnu, GTK+ Version 3.24.24, cairo version 1.17.4) of 2021-02-04
Org mode version 9.4.4 (release_9.4.4-253-g4d463e @ ~/.emacs.d/straight/build/org-plus-contrib/)

[1]: https://github.com/fniessen/emacs-leuven-theme/issues/45