Great addon!!!
I agree with "Anonymous user e7e7c7" & the Developer: we should be able to choose from where to pick up the color theme.
(e.g.: FavIcon, Page's First Top-left pixel, Page's First Top-Center pixel, etc).

I don´t know if it would work on pictures or on pictures with degrade, however...

Anyway, great job (5 stars for considering the idea mentioned by "Anonymous user e7e7c7" )!!!