I've heard of this problem, and it's not the timer but something in the color head circuit to do with an internal relay. Several of the folks relating this problem also experience failure of that relay and how to fix it with alternate parts as this one was not available any more. I'm not sure if it as in Apug threads or not, do a search of the threads and see what falls out of the tree.
One thing also you want to check the wattage of that color head against the load rating of the timers relays, it shound be printed on the timers case somewhere, usually the backside.