Change Viewer Background Colour when using an Adjustment Lay

I'm using V20 and was pleased to learn about the ability to change the viewer colour to Alert Red. Unfortunately, I now understand it doesn't work when there is an adjustment layer above the clips. Is this a known problem?

I'm using the adjustment window to position a grid over a number of clips so I can move them all to centre the same place, which sometimes necessitated moving the clip exposing the background. Simple enough to then zoom to correct but ONLY once you notice, just where the Alert Red background would be useful.

Many thanks

John