As requested, I decided to use the Mario Kart Wallpapers intended for mobile devices and tile them to be used on computers. Just look for a resolution that matches your screen and browse the 7 available colors.
Enjoy!
red: http://i.cubeupload.com/t6qPly.png
2880 x 1800
2560 x 1600
2560x 1440
1920 x 1200
1680 x 1050
1440 x 900