Right click on your Desktop > Click on "Personalize" > click on "Background"

The next page will say "Personalize your background"

To the right of that will be a drop-down menu, click on it and select "Solid Color"(you could also select "Picture" and add a picture for your background)

Then select the background color you would like to use and that should do it.

Then close out the settings page and the desktop should be the color you selected.

__________________
If it ain't broke, fix it till it is!