Fix mismatched background in Dolphin

When running Dolphin under something other than Plasma, it is possible the background color in the folder view pane will not match the system Qt theme. This is because Dolphin reads the folder view's background color from the [Colors:View] section in ~/.config/kdeglobals. Change the following line to the RGB value you prefer (it may be given in the form #RRGGBB or R,G,B):

~/.config/kdeglobals

[Colors:View]
BackgroundNormal=#2E2E2E

If you get a blue border around the folder view pane (if you are in split view it will only be around the focused pane), you may get rid of it by applying the fusion-fixes.qss style sheet via the qt5ct app. This answer describes what to do to get the adwaita dark theme working for dolphin under Gnome.

Alternatively, use kvantum to manage your Qt5 theming. For instructions on usage see the Kvantum project homepage.