Yeah. Red ink all but disappears under red lighting. Green isn't too crash hot either. Using pens on plastic forces you to carry extra stuff for erasing it (special wipes or solvent+cloth, or another marker to write over & wipe off) and probably different writing sticks for the other things you write on. A pencil only needs an eraser on the chart & your thumb on the whiz wheel. Many have them built in. Use a propelling pencil & you don't even need a sharpener.
Soft-ish pencil are cheap, last a fairly long time, are easily seen & erased, don't significantly wear out the map and can be used to write on just about anything you might need to scribble on. I have WACs that are 20+ years old that are still serviceable (not for man made obstacles, of course, but mountain ranges don't move much).