I don't know what the official reason for red vs blue is, but I know up here in Canada's military we usually use red because using a blue light would render the blue Grid Lines and numbers found on our topos invisible. <br><br>Being in the artillery, I've seen some of our Warrant Officers use a half red / half blue filter for our flashlights though I'm sure that was mostly an aesthetic thing, as the artillery colours are red over blue. <br><br>Ironbird