I have both Yellow and Clear accessory lights on the 4Runner - and there is no question that yellow is better for FOG or SNOW. Why am I so sure? I also used to have a second pair of Yellow Driving lights mounted on my brush guard (also gone now). They were equal in size and brightness to my headlights, only yellow.

In heavy snow or fog, I would simply turn my headlights off, driving with nothing but yellow. One night in Lake Tahoe I had 5-6 cars pull off the shoulder one-by-one and follow my all-yellow lights back into town - and this after each had given up on visibility! I swear by YELLOW LIGHTS!

BTW - No one had brought up the importance of beam pattern and proper aiming. Both of my yellow's have/had Horizontal cut-offs in their beams, so they did not produce light above the horizon. My clear's by comparison have a more traditional driving beam. (I have, for the record, tried clears with a proper cut-off - but am not impressed).

Scientific or just a Placebo? Don't know, but my eyes tell me Yellow is way easier. Oh ya - anyone own or use Yellow glasses from time to time? I do, and they work the same way - reducing eye strain under low light daytime conditions.