While google has been working on implementing visual search within their mobile devices and Android OS, Idée Labs has created a great way to search millions of images based on colors, alike images, and BYO ('Bring Your Own').
Multicolor Search
Try for yourself

The Multicolr Search is a playground for findiing images that contain the group of colors of your choice. Using the Multicolr Search Lab, your able to browse through 10 million of Flickr’s most compelling images and discover the images that contain the colors of your choice. You can choose from 1 up to 10 colors combined from their palette of 120 different colors and the Multicolour Search lab will return images that meet your criteria.
Visual Search
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The Visual Search Lab allows you to search through nearly 3 million stock photography images from Alamy by selecting a single image and it will return as many alike images as it can find. It locates images that are simliar just by clicking on them. You can also combin search terms, to further narrow your results and locate the exact images your looking for. These images then can be purchased, if you desire, at www.alamy.com
BYO ('Bring Your Own') Search
Try for yourself
Similar to the Visual Search Lab, the BYO search directly caters to the image of your choice. You can either upload your own image from your computer or choose an image from anywhere on the web. After uploading your own image or selecting and image URL's path on the web, the Idée Labs returns similar images from the nearly 3 million stock photos from Alamy.
We selected this image:

And the BYO search lab returned the following:
