SUMMARY After 4ebeb509 [1], any background (without set colour?) will be painted with the widget window colour, so for example something like a plain text file will be rendered with purple background instead of white (using the default theme of Falkon), if window colour was set to purple via, for example, the LXQt 'Window Color' setting in LXQt Appearance Configuration/Widget Style. This also affects times when a new tab for example is opened: the window will flash with an unexpected colour. STEPS TO REPRODUCE 1. Set widget window colour to '$someColour'. 2. Observe the normally white (default style) backgrounds be painted with '$someColour'. OBSERVED RESULT Backgrounds are painted with widget window colour. EXPECTED RESULT Backgrounds are not painted with widget window colour. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Gentoo Linux/git master KDE Plasma Version: git master KDE Frameworks Version: git master Qt Version: 5.15.1 (5.15 git master) ADDITIONAL INFORMATION 1. https://invent.kde.org/network/falkon/-/commit/4ebeb509b75b8ca2ce494d30d8f60ddcf124e9f2
The change was reverted. The idea behind it looks good and it can help in some cases, but it needs a bit more tweaking and toying before going to production. Thank you for reporting.