Who has jurisdiction over the waterway?
You may find that you need to comply with Coast Guard rules if you operate on waterways with commercial traffic or "documented" vessels. Here in Chesapeake Bay country, I get to see a few boats, including some Biiiggggg ones! All have one thing in common with lights, A Red light on one side, a Green light on the other, and a White light on (or close to) the highest point on the vessel. All lights are steady (not flashing) and are called "running lights". My thinking is that if those are required for that purpose, then the use of Red, White, and Green are somewhat restricted and blue comes up as a logical choice for "Emergency" vessel identification. I have also seen towing and salvage boats with amber flashing lights. Stay Safe....