Because color is reflected light, sensors can detect the color of a surface. With some creatively applied tubing, the direction of light can be detected, too. And if fire is the thing for your bot, there is a sensor for flame.
Do you want to measure human movement with infrared (IR) light? See Experiment: Burglar Alarm! (Passive Infrared Sensor). Need to know if an object is nearer than a given distance, using IR? See Experiment: Detect Obstacles With Infrared (IR Distance Sensor).