With regards to the color of the light and night vision it's good to remember that the amount of light is very important as well. Any color light that is too bright will over power night adapted vision.
There are several different colors used at different levels of brightness that suit different tasks. There is no one color that works for all situations. So while red, green, and even blue LED's are becoming more popular on headlamps and flashlights as well, they might be a fad but they also really can serve different purposes especially with adjustable levels.
For example, reading a map with a red LED can work great for preserving your night vision but is useless if the roads are marked in red. Green light works better in that case. Blue is used for finding blood trails while hunting as the blood shows up as dark and even black spots that really stand out. Green works well with maps as I said above, but adjusting a telescope or using a star chart is done better with red. There is no one best choice for all tasks combined. Practical usage tends to develope practical solutions, and demand drives the market.
I am more concerned about the amount of brightness for headlamps like this. Not all tasks require 100 lumens of white and other colors tend to function better at far lower levels for the tasks for which I need a headlamp.