I'd forgotten completely about this tool, so thanks to Gerrie Congden for flagging it up on the twelveby12 blog. This colour picking tool can be found at http://labs.ideeinc.com/multicolr/
Pick up to 10 colours from their palette to produce a mosaic:
Multiple selection of a single colour controls the colour balance. Once the mosaic has been created you can click on an image to see it full size. Note that all images are taken from Flickr so you will need to check the License rights, to the bottom right of the page, if you want to use the image in your work.