OXYGEN: fixes to font color icons

Change-Id: I53abb17326196dda4533dec204d8d16ef6ac9748
Reviewed-on: https://gerrit.libreoffice.org/12204
Reviewed-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>
Tested-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>