Better desktop icon colors

Summary:
The current icons with an abstract desktop wallpaper in the background have a very hard to see white icon, so this improves the colors and contrast of the abstract desktop wallpaper and the white icon.

Test Plan: Open cuttlefish and see if every icon of this type has different colors now

Reviewers: VDG, Breeze, ngraham

Reviewed By: VDG, Breeze, ngraham

Subscribers: ngraham, Breeze, kde-frameworks-devel, VDG

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D17923