This is a good question. As it starts to get dark, our pupils start to dilate "expand" to let more light in and enhances our ability to see. Granted not great, but anything you get is better than none at all.
Yellow and white light will cause your pupil to constrict. A normal person will take 22-25 minutes to get their natural night vision back. When you use red light or red filter lens to produce the red light. Your eyes will constrict, but much less than other light colors. Meaning, you should have your natural night vision in 8-12 minutes.
Basically when you are up before the morning dawn and stealthily enter your games territory, you don't want to be blind because your eyes constricted more than necessary and by the time you get your normal vision, it is too late and you have missed your games last important movement. I have seen many use regular yellow/white light and when they reach their destination they are so blind that they start to light up the area with their flashlight to see what's going on. Game will bust you and disappear. Many will say there is nothing out here, when someone else shoots a nice animal, they reply, he got lucky!
Other colors such as blue, help in seeing blood easier .
Always have at least two forms of light with you, such as a head lamp and pen light. Try to coordinate them to use the same type of batteries. Keep a couple of extra fresh set of batteries with you in an insulated compartment. Such as neopreme case. Cold will kill your batteries. Get in the habit of putting your equipment in the same place always. No fiddling in the dark to find reserves etc...
Best of luck to you.
