[Vracer111]

Light output will be yellow whether using yellow lense with clear bulb or yellow bulb with clear lense, a yellow lense with yellow bulb would be an even deeper yellow though. Yellow is the best color temperature for fog lights as it will provide you with the best contrast even with a lower lumen level than white - too much light is actually a bad thing, you loose contrast and detail with a bright white light and you are dilating your pupils more.

Same thing for yellow or amber shields on a helmet, make the contrast pop greatly and you can see every little thing on track...first thing that goes on any new helmet for me is an amber/yellow shield. Yellow light is a much more functional wavelength than white for any lighting needs where you want more clarity/contrast and to see greater depth perception in your vision. If you just want to light things up at a farther distance while blowing out the contrast and not care about the loss of both detail and perspective, then white is fine. Personally I'd never go with a white light wavelength for fog lights... especially when used for actual foggy conditions.