Move your mouse to the right upper or right lower corner or swipe from the right.
Click on the wheel icon (lowest icon)
Click on Change PC settings
Click on Personalize.
Slide the slider to the one of the first four colors.
As you can see there are 21 background colors and around 18 fore ground colors.
In the beginning I thought, I could not change the Windows 8 start screen color to black because I focused on the little colored foreground squares, and they don’t contain the color black.