When using an Apple desktop or laptop that is running the Mac OS X operating system, you navigate the folders and files on your hard drive using an application called the Finder. By default, all Finder windows are displayed as icons on a white background. However, you can customise certain colour settings in the Finder's preferences and change the background colour of Finder windows to black.
Open a new Finder window by clicking on the "Finder" icon at the bottom of the screen.
Go to "View" in the top menu bar and choose "Show View Options."
Select the "Color" radio button in the section of the window labelled "Background."
Click once on the white square that appears next to the "Color" radio button.
Highlight "Black" in the colour palette window.
Click on the red X button in the upper-left corner of the colour palette window to save the settings and make the background of your Mac's Finder black.