How to get this effect...

[AJCupples]

I'm a Gimp novice, so I need some help...

http://www.johngreenbooks.com/ <-- on this author site, on the main page, there's a blue and yellow photo of John Green and I was wondering how I could get an effect like that on my own pictures?? I've messed about with a few things, but they failed badly. Can anyone help me, please?

Thanks in advance.