Quite a while back, I posted about the fact that it doesn't matter what colour is chosen for the background, when run in kiosk, the background is white. Afraid this is still the case.
The work-around was to put a coloured frame behind everything, but that doesn't work when resize doesn't work and you've got your little subtle dark-background 1024x768 rectangle in the middle of a large field of white on a 1920x1080 monitor.
I'm going to download the test version (viewtopic.php?f=12&t=3135), but it says that it's not for a production environment, and even if I design the virtual console on a different machine, I'll be running it on the latest Raspberry Pi version (qlcplus_4.12.2_armhf.deb). (Alas, Rasbian Buster doesn't have the same pretty fonts that Fedora has).
Q Light Controller+
Official forums of the QLC+ project