Remember color scheme from loaded pptx file
or use default values.

Change-Id: Icb69c51603afc5f332c20c75e4ed5f659f4b5614
Reviewed-on: https://gerrit.libreoffice.org/43470Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Szymon Kłos <szymon.klos@collabora.com>