Here is what I've found on regulations:
All vessels should use proper navigation lights. However, non-powered vessels, such as canoes, kayaks, rowboats, and sailboats under 7 meters in length are not required to have lights installed, and may use a flashlight for navigation. The light does not have to be turned on at all times, but should be turned on in time to avoid a collision. (Rule 25)
I've also thought that I could tie a small strobe to the top of the mast (I have one that I wear for emergencies on my life vest when I race "big boats" at night), for added visiblity (and should also have another handy on my own life vest).
just a big torch aimed onto the sail will be more than enough for other boats to know you are a sailboat ... and they won;t hit you ...
when you shine the sail .. both sides will light up.... giving the light an omnidirectional outcome... that is all you need.
the red and green lights are not necessary... nor are they a legal requirement.
...I sailed my Laser at night in a 24 hour endurance race...
If you're worried about night vision then simply shut one eye before you turn on the light and keep it shut until you turn the light off. But since the first post mentioned there is a lot of background light keeping your night vision probably isn't going to be a huge issue.