Color Wiggle is a Utility plug-in that let's you wiggle between colors easily. Just set the colors you want to wiggle between and adjust the wiggle params. The plug-in automatically wiggles between those colors and also produces a 'color-out' parameter so you can link it to other effects. You can also loop the wiggle values. For more info, checkout the product page.
Color Wiggle is no longer a paid product and now available for free!