If the processor is 100% in use, then the bottleneck is in it. Probably 4 colors are insufficient if it gets so slow. Just make sure you don't have any other CPU consuming processes. Also monitor the temperature to see if you are not using a thermal accelerator.Leaving it below will show only the processor bottleneck. You can leave high / ultra for better graphics, but the overall performance will not be very good if the CPU is insufficient for this type of game.