Colour of light emitted
The colour of light emitted by vehicle lights is largely standardised by longstanding convention, first codified in the 1949 Vienna Convention on Road Traffic and later specified in the 1968 United Nations Convention on Road Traffic. Generally, but with some global and regional exceptions, lamps facing rearward must emit red light, lamps facing sideward and all turn signals must emit amber light (though in North America rear turn signals may emit either amber or red light), lamps facing frontward must emit white or selective yellow light, and no other colours are permitted except on emergency vehicles.