Hardcode fewer colorSets

Summary:
We were overriding them on the background only and it would play weird with the
feature where the toolbar looks the same as the page.

BUG: 421571

Test Plan: Still feels a bit random that it keeps changing but at least it looks consistent.

Reviewers: #plasma, ngraham

Reviewed By: ngraham

Subscribers: ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D29784