Colorful, Classic and HD themes are available on every Gmail account. You can browse through these themes and activate them with a simple click of a button.
Up until now, there was no way to add a picture as your background image on Gmail. Now you can create your custom skin, all thanks to the new Custom Themes feature.
Go to the Themes page, select Custom Themes (Light and Dark available). You can add your own background image, or upload a high resolution photo from your phone.
You can also paste a URL, or select quality images from the Featured section that has some quality, free-to-use wallpapers.
Once the background image is selected, the theme will be activated on your account. It is recommended to select any picture of at least 2560 x 1920 px resolution.
Note: The inbox messages will overshadow the background image, which means the background image will not be entirely visible.