[BUGFIX] Make icon color white for colored buttons

This patch set the icon color for colored buttons to white instead
of black. And fix it for the clipboard clear button.

Resolves: #71032
Releases: master
Change-Id: Ie145388430477dc17fba520e0dd6089db67bdf23
Reviewed-on: https://review.typo3.org/44283


Tested-by: Michael Oehlhof <typo3@oehlhof.de>
Reviewed-by: Michael Oehlhof <typo3@oehlhof.de>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>