It's no secret I love StumbleUpon but every once in awhile I come across a gem that I bookmark, this was one of them. It's MulticolorEngine. What is it exactly? In their words,"We extracted the colors from 10 million Creative Commons images on Flickr. Search this collection by color. Addictive and very likely the best color search engine in the world*!"

Addictive is right. You pick colour combinations (up to five colours) and adjust the hues to your liking to make the most beautiful images ever. 

I don't even want to tell you the number of hours I've wasted. Don't say I didn't warn you.