Not too long ago Gmail setup a way to change the way that you see your Gmail account. Before this, there were third party addons that allowed more themes. Unfortunately those addons could have hacked your Gmail account. Gmail now features over 30 themes to choose from. I wish there was a custom theme maker but there are only preset themes.

Follow up:

To change the theme of Gmail click settings up in the top right corner of GMail then click the themes link.

You will see several different themes to choose from. Pick which one best suits you.

Below you can see the Ninja Theme.

Now you know how to change the theme of Gmail. No longer will checking your email be boring.