Background color issues

[luzpaz]

OS: Ubuntu 20.04.4 LTS (KDE/plasma)
Word size of FreeCAD: 64-bit
Version: 0.20.
Build type: Release
Branch: unknown
Hash: ef37abc4413f343a922964447ff1a4d21ce37ded
Python 3.8.10, Qt 5.12.8, Coin 4.0.0, OCC 7.5.2
Locale: English/United States (en_US)
Installed mods: 
  * A2plus 0.4.56
  * fasteners 0.3.41
  * FeedsAndSpeeds 0.4.0
  * Assembly3 0.11.3
  * Assembly4 0.11.12

Ref: https://forum.freecadweb.org/viewtopic.php?f=34&t=68700&p=595389#p595389

[turn211]

Fixed