Firstly, I like it.
It's an elegant solution that gives excellent results and works as it says.<p>Secondly, I don't like it.
In the general case, this is not something that should be left to the client to calculate - whenever you are serving the image, the server ought to know what the dominant colour is. Why make the client calculate this every time the image is displayed?<p>This is a case where JavaScript harms the user: a JavaScript/jQuery solution to this has significant potential problems: there are numerous cases where it will break, some of which are identified in the other comments.