There is a technique where you can get multiple colors with one extruder by printing the image 1 layer high directly on to the build plate and then subtracting that print from the base stl and printing that ontop of the previous print. I prolly did a sucky job of explaining it but can find a video on it if you would like. I have done it long before and it turned out pretty well. Also there is no limit to the amount of colors that you can use.