There's a machine called The TomatoTek that uses "light reflection technology" to separate red tomatoes from green ones as they roll down a conveyor belt. There's a great video showing the green ones getting rejected.
This isn't the first machine to do this but it's the most advanced. It removes 98% of the green ones, and it also has GPS, radio-frequency identification, and wireless remote control.
(Search for "This Machine Color-Sorts Tomatoes By Itself.")