Well, this is not one of those tricks which is going to change your Internet-life forever but well, it is worth being told. Google Image Search can be restricted even further by using a new, specific string...
In fact, now you can search images by colors thanks to the following strings: “imgcolor=green” or “imgcolor=blue,red”. Here is an example: http://images.google.com/images?imgcolor=red&hl=en&q=house. Of course you can change the color red and the keyword house with anything else you like!