Picture Paint by Danny Guo

Dynamic theme that uses the color palette of the current National Geographic Photo of the Day. The theme automatically updates every day, and you can click the toolbar button to see the picture and click through to the National Geographic page. You can also view past pictures and themes by changing the date in the popup. If you'd like to turn off the automatic updates and keep the theme on a particular date, change the setting in the extension's preferences page.

Note that Picture Paint will need permission to "Access your data for all websites." This
permission allows it to use the canvas API to process the image and determine the color palette. As far as I can tell, there isn't a narrower permission that I can use instead. Nevertheless, Picture Paint does not read your browsing history or send your data anywhere.

The source code is available on GitHub.