In LibreOffice and MS Office, there are two types of colors:
 - Automatic (which is taken from settings) and Fixed (which is set by RGB value).
OOXML is setting automatic color by default, by not providing any RGB color.
To preserve automatic color we need to not export
RGB color during OOXML export.

Change-Id: I8895230c4fffc9d8741f3eff37e64c4823d71da8
Reviewed-on: https://gerrit.libreoffice.org/37970Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>