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
