Remove hardcoded colors
Summary:
Fixes https://www.reddit.com/r/kde/comments/f2mxd3/517_seeing_weird_white_corners_on_my_autohiding/
BUG:417511
Reviewers: ndavis
Reviewed By: ndavis
Subscribers: kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D27354