I would have to say that black is the hardest color to see at night. A coworker unfortunately found that out the hard way when he was drunk and crossing a roadway at night while wearing black clothing. He was hit by a car.
However, as this guy puts it:
“When our eyes are fully night adapted, we are using our rods. The rods cannot detect red light, but our cones can. So if we use a red light flashlight we can see what is around us using our cones. The rods in our eye can’t see the red light and our night adapted vision is unaffected. Turn off the red light and you can go right back to looking at the stars in the same detail as before without having to wait another ½ hour for our rods to work again.”
To totally trash someone’s night vision he says shine a bright turquoise or cyan light at them:
“If you want to thoroughly ruin someone’s night adapted vision, shine a bright Cyan/Turquoise at them. Since the rods are responsible for our night vision and are most sensitive to this color light, they’ll immediately go “night blind” and will be unable to see in the dark at all immediately after turning off the light. Of course this will work with a bright white light too.”