Experiment: HTML5 Image Editor. See it working at: http://felipenmoura.org/labs/html5-imager/
This tool helps you changing the hue and saturation of images, as well as it can be used as a color picker. You can also pick a color, and remove all the pixels in the image that correspond to that color.
Check this out on github: https://github.com/felipenmoura/html5-imager