A few months ago Google enabled the theme option for Gmail.
Users can preview and select one of the available themes to change their inbox appearance.
This week, Google has added a neat option to completely customize the theme colors, and create a unique theme.
You can find the option in Settings -> Themes.
Look for the “Choose your own colors” link as shown in the screenshot below.
A pop-up window comes up, where you can start choosing your favorite colors.
It would also be cool if images could be added on the custom theme (same way as on the preset themes).