Do you know about Gmail's Custom Themes

Google announced custom themes can come back to Gmail that enables users to upload their own background pictures (or choose from Google+ photos), browse from a variety of “Featured Photos,” or enter a URL of any image.

To try the new feature, click the "settings" button, select "themes" (or use this URL), scroll right down to "custom themes", click "light" or "dark" and choose a picture. you'll choose one amongst the good featured pictures from Picasa internet, select one amongst your photos, use the search feature, upload a picture or paste a URL. the same interface is employed for Google homepage's custom background feature.