Door: kelbytv.com/photoshopkillertips
Using the hue jitter settings.
http://kelbytv.com/photoshopkillertips/2009/11/08/hue-jitter-for-brushes/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+PhotoshopKillerTips+%28Photoshop+Killer+Tips+%28Video%29%29