Just a small addition to the good information John presented,.   Any sailing vessel, regardless of size, in addition to the side and stern lights can carry a red over green all-around lights high on the mast.

The rules also allow for any sailing vessel that is less than 7 meters may show only a white light in sufficent time to prevent collision...but I don't really recommend it!

I have a tri color masthead Aqua Signal light wihich also has an all around light which I use as an anchor light.  I also have the original deck mounted red/green lights, and have added a white light part way up the mast for when motoring.  I am going to change the deck lights to a bow mounted re/green light, mainly because when I drop the sail, (i use a downhaul from the cockpit) the sail usually hids the lights.  I also upgraded the stern light to an Aqua Signal just for increased visibility.  All the lights are the Aqua Signal series 25 navigation lights.

John Edwards
Miss T
M17 # 372