Fix fdo#84512 Background color not shown in Styles-Dropdown

this fix is only for simple color backgrounds; gradient, hatching and bitmap are not implement.

Change-Id: I5ec31c0105491c6d27835d63648fedff21998926
Reviewed-on: https://gerrit.libreoffice.org/11762
Reviewed-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>
Tested-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>