This seems like a feature Google should have had all along. When browsing images you get the option to select similar images based on results.
I still prefer Flickr, here are some Flickr and non-FlickrTools.
Select up to 10 colors and get image results that use that palette. Pretty cool.
Unsure how this site does it, but it generates search results twice as fast a search on Flickr itself, even displays the pixel dimensions of the largest version of the image available. I use this site ALL the time.