XnView Software

XnViewMP 1.8.8 64bit
Windows11 (24H2), display resolution 3840x2160, win scaling 150%

Browser/Viewer - theme switching
viewport background of active tab keeps color of previous theme

to reproduce
1. open Browser (OR Viewer) tab
2. goto Settings
- change theme from Default to any other
new theme will be applied - OK
- press OK to close Settings
'Please restart' popup will appear
- press OK
viewport's background of active tab (Browser>Preview pane OR Viewer) will revert to the color of previous theme

Thanks to your detailed description I can reproduce the problem.

This problem is supposed to be fixed in XnView MP 1.9.0. Please check and confirm the bug fix here.

fixed in 190