title: make HTML background always changing
body: <p>What do I mean by 'Always changing'?
  Well, for example, the Windows 8 installing screen, you see a text at the middle that says:'You can get new apps from the store', and the background are changing from red to orange to yellow to green to cyan to blue to purple then to red.
  I mean, how do I do that to my HTML background with JavaScript?</p>