I use dark mode on both my iOS and Android devices. When I use certain colors to mark my songs (yellow, orange, light blue) they show up fine on these devices but become hard to read in the web interface. So it would be nice if the web interface too would offer a dark mode.
Is that the only reason you would want this? Can you attach a screen shot showing where the song colors are hard to read? BandHelper does display slightly different shades of the song colors depending on whether it's in the dark or the light interface.