This simple RGBled color mixer uses NO microcontrollers( Arduino - Pic etc ). It controls the brightness of each color channel by varying the duty cycle (On time vs OFF time) by a technique named PWM or pulse width modulation. This results in a very low power dissipation, as leds are either fully on or off. The circuit manages the three channels with only 1 common integrated circuit and 2 transistors.
Step 1: RGB Controller at Work
Step 2: Complete Circuit Diagram
IC1: TL084 (quad FET input op-amp)
Q1: BC558 (general purpose PNP transistor)
Q2: BC548(general purpose NPN transistor)
VR1-VR3 10Kohm Linear potentiometers
LED: RGB common cathode led
Step 3: PUT Oscillator (sawtooth Generator)
Step 4: Comparators 1-3
This in turn determines the time each led will be ON during each sawtooth oscillator cycle, making it appear to be brighter or darker to the eye.
Step 5: Driving RGB LED
For this demo I am driving the LEDs directly from the OP-amp, but you can drive any power leds, by adding a power mosfet or transistor.