The way to user adjusting a control to get the color of front light you want is applied use of color additive theory using different intensity of 3 primary color lights, (blue, green, red) to get any color. This is how color TV works and is now easier than ever with LED lights and digital switching of each individual light. This could drain battery a little faster than existing front light.
http://www.geog.ucsb.edu/~jeff/115a/additive.html
http://en.wikipedia.org/wiki/Additive_color