After the PremultiplyViewportframeBackgroundColor FFlag was pushed in 0.691.0.6910866 it seemingly broke the way that the BackgroundColor3 property was being rendered. It now no longer renders ontop of the objects under the viewport. I have attached a simple repro place and some visual examples of the issue.
To repro simply disable the flag and press play on the attached repro file, and then enable the flag and test again. There should be a clear visual difference between the two.
This is when it was working prior to the flag being enabled
This is after the flag was enabled
Attached below is a simple repro place file.
ViewportBugRepro.rbxl (67.9 KB)
Expected behavior
I expect the BackgroundColor3 render behavior on the ViewportFrame to be 1:1 with how it was prior to the flag being enabled.