Hope I'm never on a level crossing when you're approaching!
I use red or amber. I find red sometimes helps with Foxes or Rabbits that've been lamped before. An amber filter doesn't reduce the beam length as much as other colours, and cuts through any mist better. I personally find that amber also gives a better contrast which makes spotting at distance easier
I have tried them a few times and always seem too be more of a hindrance too me and don't worry I hate driving