"...blue shows up particularly well.."
Many years ago I read an article in a gun magazine, guy was a shooter and photographer, complete with darkroom. He got a bunch of cards in different colors, and a bunch of different people. Using his enlarger, he could regulate the time and intensity of the light hitting the colored cards. Long story kindasorta short, the color them most people could recognize fastest with the least amount of light was blue. I was working a lot of graveyard shift back then, I tried it by painting the front sight of my S&W Mod 28 baby blue instead of red and it seemed to work. At least for me...
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OBG