I found this article about using red light to preserve night vision. It says in most cases blue-green or a dim white light is best to preserve night vision. I have always been under the impression red was best after reading it all over the net. I am still not sure what to think.
thats an interesting read , I use red filters always when hunting hmmm maybe I need to try blue
I find red light seems to mess a little with my perception of things ..ie things looking much larger under red light than they actualy are ..Im not alone my hunting buddy agrees he has a hard time with depths size range ect when using red filtered light
To me the key is using the dimmest light I can get by with .
The American Optometric Association has a pretty in-depth article on their site as well...
Corrected link... Nutz
Bad link.
Sorry about that... corrected link... working now. 
Green.
It's not a myth. The issue is that people usually mix what they are talking about on this issue.
Red is the best color for preserving night adaptation. Rods aren't sensitive to the red spectrum. Night adaptation refers to rods as that is all you are using when it's really dark. Therefore red is the correct answer and is not a myth.
You can use red at a higher level which will stimulate your cones which is what we use to perceive color and for visual acuity (reading). Once you turn the red light off the rods still have not been affected so you still have dark adapted eyes.
If you look at two lasers at night (both 5mw) with one green and one red they have the same output. You see the green one much better. You even see the beam itself and not just the dot at the end. This is because your eyes are more responsive to green than to red. It just doesn't mean that green is better for preserving night vision.
If you don't use red then any light at a low level (including) white does the same thing as far as minimizing the impact on night vision. Red is the only color that doesn't impact it at all.
You can't focus as well with red and if any light (including red) is too bright it affects your cones and causes an after image but this goes away in a few minutes whereas stimulating your rods and then going back to a dark environment takes 30 minutes to an hour or longer to adapt.
So, if you are really talking about dark adaptation the answer is to use a red LED.
However, many people aren't really talking about this. They are talking about what color of light can they see best at night at the lowest level. This would be cyan or blue/green. The eyes are most responsive to this color. This has nothing to do with dark adaptation however.
If you turn the cyan light off, your rods have been very stimulated and will take a long time to recover. Not everyone who is outside is using their dark adapted eyes however. If you are using a flashlight the entire time this isn't about dark adapted eyes.
at a distance red is less visible than other lights. thats really the main initial use, course it seems to preserve night vision also .
its not as visible which makes it disorientating to some people- think it makes things look flat.
frankly a colored light, red or blue/green, seems that it just doesnt blast all your light receptors. so a portion can be more sensitive to low light faster
Other than red, it's not the color but rather the lower level that is partially preserving some night vision. Green stimulates your rods the most which is why people like to use it. Something that simulates the rods the most however is the opposite of preserving night vision.
Therefore it isn't the color (except for red) but the low level that you are using it at that is doing the trick.
The reason you don't see red as well is because the rods aren't sensitive to it at all (they don't know it's even on) and the cones aren't as sensitive to it as to green.