hopefully shedding a little light on the off-topic (couldn't help myself):
if we were talking about headlights, perhaps white is better for most people - there is a long standing debate, but i think it has more to do with manufacturing cost than human visibility issues
but we are talking about fog lights
our eyes are very limited in the spectrum of light it sees best - the human eye sees yellow and green much better than other colors - longer wavelength light (yellow) scatters differently and less than shorter wavelength light (blue) - varying wavelengths gives better definition - adding yellow light is far more effective than adding white light, especially at picking up peripheral objects - it's not a reflection issue as much as a scattering one - granted that any "filter" in front of the light cuts down on its penetrating power, but power isn't everything - too much light can be as much of a problem as not enough
the key is in providing light more tuned to the rods than the cones - rods are for night vision cones are for day vision
we have about 6 to 7 million cones, red (64%), green (32%) and blue (2%) - the blue cones are the most sensitive, but we have the fewest - this is why blue light at night is "blinding" - the cones are responsible for all high resolution vision, but rely on eye movement to keep the light from falling on the fovea centralis, where the bulk of the cones reside - we tend not to move our eyes as much at night, making this particularly complicated
we have about 120 million rods - the rods don't see color but are excellent at peripheral vision - they are also shifted toward shorter wavelength light than the cones - this is why as it becomes dark, it is easier to see green than red - they are also much slower to react than the cones, and peak sharply in response to blue light, taking as much as a half hour to attain optimal night vision, which is why bright headlights temporarily "blind" you at night - this is why yellow light works better than higher wavelength light at night
consequently yellow light makes for a better fog light, and probably a better headlight too
rods also don't see red - this is also why instrument clusters are better red for night vision than any other color - anything shorter in wavelength only detracts from the eye's ability to distinguish other objects at night
there is a 400 page study on headlight color, brightness and glare that the government has available to you - very dry but very informative
as for lens inspection, talk to the guys in states that go through this - they can't register their cars if their lights aren't aimed right, the right type, and fully functional - my ticket was $180 is 1992 for having non-DOT headlights - we don't have inspections here, but the cop was pissed off and nailed me for it
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