Or you can go back to basics and build this reflective RGB sensor from an LED and a photocell. The principle behind [TechMartian]’s approach is simplicity itself: shine different colored lights ...

The circuit produces 490…520 mV on 2k load @ 20 mA current through the LED. This is more than enough for several micropower op-amps such as the AD8603/AD8607. The output voltage of the photocell can ...