Function
The front and rear lights on a vehicle serve several purposes. The front lights are used to illuminate the foreground for the driver and to make the vehicle more visible to oncoming traffic. The rear lights do the same for following traffic, in addition to communicating the driver's intent to turn or slow down.
Color
To help distinguish between receding and oncoming traffic, front lights are often required to be a different color than rear lights. Front lights are commonly white or amber, while rear lights are almost always red.
Bicycles
Bicycles are generally required to have lighting attached only if they are being used during hours of low visibility, such as at night or during certain weather conditions. In addition to lights, bicycles always are required to use front and rear reflectors.