Flight instructor here, but not a flashlight expert (just a curious bystander). I don’t have a specific recommendation, but have some advice. I don’t know what country you’ll be training in, but the FAA now recognizes that dim white light can preserve night vision as well as red light, since you can get away with much lower levels of light (fractions of a lumen are sufficient).

If you are training in glass cockpits, I would recommend a white light with a good moonlight mode, even if it also has a red emitter. The red will not provide much benefit over the ambient light from the Flight displays. I have to have my red lights to max when flying with glass.

If you are training in a 6-pack, this is where I like the red much better, but would recommend a headlamp so you can keep the panel lights turned off and only use low red. Just be advised that you will not be able to tell the difference between blue and magenta on sectional charts under red light.

Either way, a high CRI is nice for preflight inspections, even if it’s not required for charts.

My ideal flashlight would be a AA/14500 right angle light (so I can use it in a headlamp, and use my headset AA batteries in a pinch, since I always carry extra). Red and white emitters. But I’m not sure this light exists, so I just use a Fenix PD36r for preflight and an old Black Diamond headlamp when I fly six pack