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.
We extracted the colours from 3 million “interesting” Flickr images. Using our visual similarity technology you can navigate the collection by colour.
2. CompFight
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.