I hope you guys don't mind a long post. I read up a bit on night vision and cockpit/instrumentation illumination while I was retrofitting an E39 dome light to my car.
Any light that is bright enough that you perceive color is also bright enough to reduce your night vision. The rods supply your grainy (ca. 20/200) night vision and are what you wish to excite as little as possible; the cones provide color and detail. The rods and cones have roughly the same sensitivity to red light. In the blue region, the rods are about three orders of magnitude more sensitivity than the cones. When you increase the brightness of a blue light high enough that your cones are perceiving color and detail, you are really hammering on the rods and your night vision. But you can tell this, because the blue light appears that much brighter than red light of the same (radiative) intensity.
The advantage of red light (650 nm+) is that you don't have to increase the intensity nearly as much before you excite the cones and perceive color and detail. Thus you can read things and see color under red light at lower intensities, lower intensities that excite your rods and affect your night vision less (assuming you have uncorrected, youthful vision -- more anon). That does mean, however, that red light will also appear much dimmer. If you now crank your red light up to match the brightness you perceive from blue, you are back to the same, high, radiative intensity and disturbing your night vision just as much.
Thus, the important point for preserving your night vision, is to dim the light -- be it orange, blue, green or whatever -- as much as possible.
Another advantage of red is that it is weakly perceptible in your peripheral vision which makes it less likely people will notice red instrument and cockpit lighting from outside. That should also make it less distracting when you are looking down the road.
Red light, however, has some disadvantages. It refracts less (I think I got that right) and focuses further back on the eye, pushing your vision about a diopter toward far-sightedness. If you are far-sighted like me, that is an extra diopter you have to accommodate, which becomes more of a challenge as your eyes age. I can compensate by increasing the light level, but at the cost of my night vision. Blue, on the other hand, focuses further forward and pushes your vision toward near-sightedness.
If I were feeling mischievous, I would alter my car to better match my vision and change all the interior and instrument lighting to blue or even violet. My near-sighted friends might find that tiring. I suppose I could offer them eye masks (and relaxing music) if that proves to be a problem. Likewise, those friends could reciprocate when I ride with them, and make everything in their cars emit a deep red.
As it is, I decided to be gracious and follow current practices in aircraft cockpit lighting. I flood the center console area with a dim, neutral, white light. (My camera has given it a bluish cast in the picture.)
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