File Selector is a Linux-only section. The closest thing I've seen in Windows - that didn't involve desktop settings - was a bizarre encoding or locale setting that made all the menus blank of text - but they were normal colors.
Try changing the colors in Windows anyway ... go to Control Panel > Personalization or just right-click an empty area of the desktop and choose Personalize. Click on Window Color, then the link Advanced Appearance Settings... In the dialog that appears, choose Menu on the Item dropdown, and make sure Color1 is something light. Then click Okay, close the other windows and restart Opera.