bnc#584721: invisible text because of wrong color (white)

Color::getColor() method uses some caching mechanism which
works wrong when the result depend on one of the input parameters.
So avoid caching in these cases.

(cherry picked from commit cfe658c289de030dc3a8fecd3bac0a0004a18061)

Conflicts:
	sd/qa/unit/import-tests.cxx

Change-Id: Ifa9221e21e685715454de86d5cec09ff6c266307
Reviewed-on: https://gerrit.libreoffice.org/11724
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>