The reason the led is dim, is because the chip is in high z. Which means there is little power going to the led at all times, even when the controller is turned off the led may still be a little dim. It will mainly do it when you have installed different colored leds because the voltage is different for different color leds. If you use a diode, then it will probably go away. Its not really a big deal if the led is dim unless your picky about it.