Actually, from what I read, this isn't the case. The color of indiglo is directly controlled by the dopants in the mixture. As stated on the site linked below, Copper and Chlorine makes blue, Copper and Aluminum makes Green and Copper, Chlorine and Managese makes yellow. You can have multiple color layers. And each layer would require it's own electrodes and it's own power source. You could then switch between the different colors.

http://van.hep.uiuc.edu/van/qa/section/Light_and_Sound/Making_Light/20010312181452.htm
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~Max