How do I know which color fog lights to use? Do I get less light from yellow fog lights?
The quick answer is "any color you would like." However, many states have regulations restricting colors other than yellow or white - be sure to check your local laws.
White will provide you with the most light output. Remember to place them no more than 20'' off the ground since fog tends to hover just above that area.
The old belief that yellow fog lamps contribute to superior lighting in foggy conditions was based on a misinterpretation of physical laws. The truth is that adding any color reduces total lumen output and therefore has a negative impact on visibility - if only by a fraction.