If you want fog lights that are better in fog it is selective yellow bulbs you need. But as there was no demand, they are no longer manufactured.
It is not because the light penetrates fog better as I thought. It is because of glare. Every days a school day.
Here is the science behind it, if you fancy a long read -
https://www.danielsternlighting.com/tech/lights/light_color/light_color.html"What, then, explains the persistent subjective preference amongst experienced poor-weather drivers for selective yellow fog lamps (whether or not they happen to know that's the name of the colour),
despite decades of white fog lamp prevalence? Selective yellow light can improve a driver's ability to see in fog or rain or snow, but not because it 'penetrates fog better' or 'reflects less off droplets'. In fact it's because of the way the human eye processes different colours of light. Blue, indigo, and violet are difficult for the human optical system to process correctly. They are the shortest visible wavelengths and tend to focus in front of our retina rather than upon it. To demonstrate this to yourself, after dark find a deep blue storefront sign or blue lights on an airport runway or something else that's a deep blue light emitter against a dark background in the absence of white light—from any appreciable distance, it's almost impossible for your eyes to see the blue lighted object as a sharply defined form;the edges blur. The blur effect is not present with nearby signs or lights of colours other than blue.
Blue also is a very difficult colour of light to look at; it stimulates the reaction we call glare. Within the range of allowable white light, bluer headlamps have been shown to be 46% more glaring than yellower ones for a given intensity of light — see studies here and here. So, it seems culling the blue out of the spectrum lightens the optical workload and reduces glare. For a more detailed examination of this effect with respect to driving in foul weather, see Bullough & Rea's study on the topic."
