IIRC, the coast guard regulations for paddlecraft require only a handheld white light visible at a minimum distance that I don't remember (1 mile? 2 miles?). At any rate, any average powered LED flashlight should do. Different state requirements might be more restrictive though.
If the boatswain had slapped you because you didn't know the colors of the port and starboard,
all it took was a glance in the mirror,
and you'd feel that slap for the rest of your life.