As Vincent and Tri commented!
BLUE! BLUE! BLUE! And use is sparingly. Like a "small" "small" tooth pick applied drop!
Also take the time to do some research on "inch pound torque" specifications on the screws or fasteners.
A lot of folks break screws by putting entirely too much torque on the screws and etc. Which on occasion can create a real problem if the screw breaks off in the weapon or mounts. Fingernail polish also works but you might want to use clear. They might think your funny using RED!