If you meant that you want a solid color for the background, then while changing your background
wallpaper, be sure to select Solid Colors
from the Picture Location
drop down menu like below. You will then be able to select a color to be a blank wallpaper.
In additition, you could check the Remove background images (where available)
box in the Ease of Access Center using the tutorial below to force nothing but a solid color background to be available. Remove Background Images (where available)
Hope this helps,