So long as we all have a boatload of WHITE lights pointed forward from the car, our eyes will not dark adapt. If there is any good reason for a co-driver to use red light, I think it is to reduce the amount of distracting light in the drivers peripheral vision. We have the red lense for our map light but just use the white since it is easier to read by - and it doesnt bother me.
Now if we were to run night rallys "commando" style, red lighting would be most helpful.
Dave Getchell and I ran last weekend's Ontario Winter Rally with me using a red head lamp. That rally starts at 10:00 PM Saturday night and ends about 6:30 AM on Sunday. Because of the need to see route instructions, rally computer/odo buttons, and rally calculator buttons all in a slightly different position on a recurring basis, the amount of white light (if a single light) to light that area would have been large and would have interfered with Dave's vision. The use of a directed red light (via a head lamp) worked well for me and Dave as well (I think).
When flying or sailing at night my eyes do adjust but we have moved to using a green/blue light as it is hard to see important things on charts with red light. In the car it is not a big deal, I have the co-driver use red just to keep it less glaring and to advoid thinking there is something over there like a car on a side road coming to get me.
I made 8 submarine patrols, most in the control room or Nav Center. No one is more religous about "rig for red" than the Navy. I know it does indeed improve night vision (periscope ops or even surface running) if your eyes have been exposed only to red for half an hour or so. After the Navy I sailed my own boats for some years and except for a few nights, being good about red only lighting helped vision...right up until that prick in a power boat shines a million candlepower white light in your eyes, because he cant see without it.
A disadvantage to using a red light for inside the car is when a Worker enters your time in a red pen, which is rendered invisible by the red light. Before you know it you're out of the control zone and your co driver is screaming they didn't enter a time and by the time you realise the navvie has to run back into the control zone to get a time, and then sees it in red.. etc etc etc
Then, trying to explain to an official why you were late at an MTC and they tell you no one uses a red light, what's wrong with you....etc etc etc....
A white light helps the Co-Driver see the time card better... at least in this case.
I think that one's eyes can be trained to acclimate to darkness more quickly. I worked in a photographic darkroom for a few years (2.5 years in high school and 1.5 years in college) and I acclimate to the dark really quickly. On the other hand, I am very sensitive to bright light.
Something like that happened to me last year in another all night brisk winter TSD (Snowy Safari)in Ontario. I gave my driver hell for coming back to the car with a blank timing sticker. He wondered what I was talking about! We wasted about 20 seconds getting that sorted out until I realized that the control people wrote the time in using red ink.
I think that for a stage rally a low, focused white light on the notes is just fine. But for a TSD event, a navie has to be more concerned about looking in various places (more odo adjustments, more timing calculations, route book to follow, etc.) which requires more light on the right side of the car. This is where I think that red lights are better, as that much white light would be a bother to the driver.