The first item in the SystemSettings is always in white color. If I select another option then it becomes visible. Please see the screencast attached for more details.
Created attachment 111749 [details] Screencast of the issue
Although your screencast is very good, I am unable to reproduce it on openSuse Tumbleweed nor with Neon. But I can confirm it on Fedora 27 (with plasma 5.12.3) => I guess it's a Fedora specific problem. Please report it downstream (https://fedoraproject.org/wiki/Bugzilla)
*** This bug has been marked as a duplicate of bug 392775 ***