I noticed that if you preview some of my wallpapers and set it as a desktop background the image will look like this!
i.imgur.com/4caFVFV.png
i.imgur.com/7R0rBna.png
http://i.imgur.com/WXGonXp.png
To fix this, you have to right click on the image and then set it as a desktop background. It will fix the problem and look like this.
i.imgur.com/NK1GGc8.png
i.imgur.com/kJ97LJv.png
http://i.imgur.com/YYrafxU.png
Just wanted to let you know