Not sure what you mean by "folder background" but if you're using the Windows Classics theme, you can right-click on your Desktop, and go to Personalize, Windows Color and Appearances, Advanced, and under Item there is a drop-down menu that has a number of items for which you can change the color, font style, size and font color, etc. One of them controls the Desktop background if that's what you meant by "folder background." If not, you can just experiment with each of them until you make the changes you want.