What color headlight for best night vision?

I disagree with the green/blue thing but you can read about why below.

A bright white light is the closest to sunlight, using this sort of light at night helps the person to stay awake better and it reaches out further which is why driving lights are a bright white light. However fog lights are usually a yellow color because yellow cuts through fog and rain better, though not sure why but most new cars with optional fog lights are white. Most yellow fog lights are in the 3000k, but the most light output and best performance is 5000K. Going above 8000k or below 4300k decreases light output significantly, though in the case of fog lights it's necessary to prevent the glare from reflecting back into your eyes. However for off road use you want a slightly warmer 5000k light because a bright white has a tendency to eliminate contrast so you can see terrain better.

Also position of light is important. For off road use it's really a good idea is to have a light mounted on the helmet, the higher angle helps see terrain detail better than a light mounted on the bars, however most off road riders use both. Off road vehicles do the same thing, a bar light mounted high in combination with their headlights.

OP, you may be asking the wrong question. Rather than "What color headlight for best night vision?" consider "What color eyewear lenses for best night vision?". There's far more research and empirical studies that support that approach, going back to the early part of the 20th Century.