Well from my little knowledge of light spectrum, apparently you want a fog light that only emits one colour, yellow.

White on the other hand is all the colours of light, and apparently disperses more when it hits droplets of fog, and for some reason that's bad. I dont know enough, and apparently there are different opinions on the whole ordeal, and you'll see most new cars use xenon lights now.

The reason i chose yellow lights was because i liked how they look, and i figured if i was going to add in fog lights, i might as well choose something that i won't see on every other x on the road.