Controlling RGB LED colour using Atmega16

This tutorial will give you a brief introduction to the concept of colors and how different colors can be produced using RGB LED. The color would be controlled using an ATMega16 microcontroller.
RGB LEDs are basically the combination of the 3 LEDs (Red, Green and Blue) fused into a single package. It consists of four pins totally out of which three of them for the three different colors. The 4^th pin is common for all three colors and it’s either Cathode or Anode.

Concept of Color
Color is the visual perceptual property corresponding in humans to the categories called red, blue, yellow, green and others. (Wikipedia definition)
We know that white light (say coming from the Sun) consist of mixture of colors. Remember the prism experiment you head of when you were in school?
 
So the primary colors of light are Red, Blue and Green. All other colors we see are formed by mixing of these three colors in different proportions.
 
When we see an object, we are not seeing the object but actually we are seeing the light reflected by the object. Confusing isn’t it?

Let’s say that you are looking at a red car. Now the car appears red to you because it absorbs the green and blue part of the light incident on it and only allows the red part of the light to reflect.
So if you see a red colored car through a green filter (which allows only green light to pass through it), then it will appear in black color (since no light would reach your eyes)
And the conclusion is that
 
For more detail: Controlling RGB LED colour using Atmega16