I can make the bottom bar (the bar that shows page number) of okular disappear by adding the below line under [Main View] of okularpartrc (found in ~/.config).
ShowBottomBar=false
However, I am interested in changing the color of the bottom bar. I mean I wanna change the color of toolbar and menubar of okular which are all white by default. How can I do that? I tried adding BottomBarColor=255,0,0
under [Main View] but it doesn't change the color.