If you click on Vert Colors it over rides your Preview Scene Settings and puts a low res sunset environment into the viewer and this cannot be turned off at all.
If you turn off vert colors it remains.
You need to close down the model viewer and re open it to get it back to using your default Preview Scene Settings.
In my preview I have an empty background all black.
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I understand, the trouble with the bug reporting system is if someone has a work around I might get it here, I wont get that there.
While it might get fixed at some point using the bug reporting system it might not. It is also a better format to track issues.