Idée has some cool technology, and Adobe uses something called Piximilar as the visual search engine in Photoshop Elements 6. It would be great to see some of this in CS products.
Try Idée’s Multicolr Search Lab. If you need an image that is within a range of colors, simply point and click to add and subtract colors, and a set of images is presented that match your criteria.
See the other cool interactive demos: Visual Search Lab, to combine tags with visual search to return unique combinations of images, and BYO Image Search Lab to upload your own images or point to one on the web to see what they resemble. (via SensoryMetrics)