This circuit is a good example of a microcontroller design using the absolute minimum of external components. The ATTiny15L microcontroller from Atmel has three of its outputs connected to an RGB LED (or three individual red green and blue LEDs) and produces changing colour patterns. There are of course multicolour LEDs with a controller already built-in on the market but where would be the fun in the ready-built version? You will certainly learn much more by building and programming the design yourself.