LoneColor for Windows
Use the free, tiny and portable LoneColor app to set any solid color you like as your Desktop wallpaper, or let it surprise you with a randomly generated color wallpaper. It has a minimal design and it is very easy to use directly from your Desktop.
LoneColor for Android
Set an instant beautiful color wallpapers on your smartphone or tablet. An infinite palette with one tap! Try a surprising random color, or copy a color code from another app or site, tap LoneColor & see it fill the screen. Free and Open Source.
FrameDummy
Get a fake window frame around any image or screen area. The frame dummy looks and behaves like a real desktop window. Use it for photo frames, messages, pranks, greetings, birthday cards, or interface testing. Don't forget to try the new Prank Mode!