I understand the US Navy uses dim red light to conserve nite vision, while the
US Army uses dim green and the US Air Force uses dim blue.

take your choice. the only common factor is nite vision and dim

Red light is also harder to focus on in dim conditions, esp. as
we grow middle-aged and our "arms shorten."

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That is definitely true. I recommend keeping a pair or two of dime
store reading glasses in your nav station along with an illuminated
magnifier.

Electronic charting on a laptop is an even better solution (paper
charts for backup of course).