Me and two other friends built an RC Car with installed color sensors on it. These color sensors would allow the RC Car to follow any piece of black tape that we put on the ground. We used an Arduino Uno Board to create this device. There are two color sensors at the front of the car, facing own to the ground so it could detect any tape. Once one of the sensors detects black tape, it would alter the motor so that the RC Car would continue following the tape.
Here is a link to a video showing the Arduino RC car in action: https://www.youtube.com/watch?v=-asKRdFoPR0