This has been a topic of discussion since after the war when a researcher concluded red light preserved night vision.
In the 1980s, it was discovered in nominally lighted airspace, (moon or light pollution near cities) coupled with the enhanced visibility provided by Strobe lights made the difference still measurable, but negligible on night adapted vision. Another factor is how red light makes focusing more difficult, contrast is lower, and eyestrain increases compared to cockpits lit with white light.
The final nail in the coffin of red cockpit lighting came about with the advent of glass cockpits, where it was discovered red cockpit lighting interfered with a pilot's ability to discern colors presented on the (then) new glass displays.
All that said and done, for airborne activities that require the absolute highest preservation of night vision adaptation, red is the preferred wavelength.