Fix fdo#58161 UI: White Paragraph style invisible in Styles Drop-Down

Use the Color-Class-function "IsDark" and "IsBright" for decision to
make a change of the font-color with DecreaseContrast or DecreaseLuminance.

The change is only in the Styles Drop-Down

Change-Id: I65ac4a0bd2f72ab95e61ce2f70bca009e4f06725
Reviewed-on: https://gerrit.libreoffice.org/11716
Reviewed-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>
Tested-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>