After making changes to folder formats, make sure you close the existing window and open a new one, then go back to the folder you are interested in, to check the results. Otherwise, temporary formats can come into play and confuse things. (They're discussed in the Folder Formats: Detailed Guide but the main thing is to just use a new window to check the results.)
If you still don't see the background you expect, hover over the format lock icon on the status bar (do not click it; just hover over it) to see a tooltip which will tell you where the current folder format comes from, which should tell you what you need to edit/disable/override to get what you want.