For a long time, when I would open the Ubuntu software center, the contents appeared blank unless I clicked on a different window. This one had me stymied for quite a while, but then I found a solution posted by The_Third from a couple of years ago:
By editing a CSS file, the software center will become visible again.
sudo vi /usr/share/software-center/ui/gtk3/css/softwarecenter.css
Change the hex numbers at the end of these lines (these are my numbers, you can use what you like):
@define-color light-aubergine #4B4023;
@define-color super-light-aubergine #1D190D;