Best thing to do is to use Paint to create a blank white canvas with the dimentions of your resolution. Once you save it you can use it as your wallpaper.
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.