Oh boy! We can debate all day. I’m a commercial boat captain and work for a ferry company on very busy, congested inland bay/waterways. And I do night paddles in my sea kayak. There’s a lot of good advise above.
I use mainly only a 360° white light. Elevated as best as possible, as far aft as possible. Here’s why: White is visible from a greater distance that green or red. A lone white light may be a stern light or an anchor light. In both cases the other boat should expect to be a “give way” vessel (though many don’t know it). Elevated makes it more visible in seas. Far aft reduces the angle that it’s blocked by my body and not shining in my face.
I’ve seen folks use red/green side lights like a power/sail boat, and would recommend against it. Here’s why: The side lights are required to show over a very specific angle and the little temp-rigged jobs don’t comply. Their purpose is to show what aspect/angle the boats are approaching at to determine who stands on course, who gives way. A kayak frequently bounces, turns and veers, confusing to other boats. A group of kayaks at all different angles (showing reds & greens) would look very confusing. I’ve also seen several cases of paddlers unwittingly mounting them reversed. On a kayak they are so low that they can appear/disappear in the smallest chop, looking somewhat like a flashing light, even a flashing buoy. That could cause confusion to an approaching power boat. Don’t pretend to look like a power boat. A bunch of whites just looks like something to avoid.
Of course if your local regs require something else, by all means follow them.
I also carry a strobe on my PFD shoulder. If I get separated from my boat I want to have a recognized, attention-getting distress signal. And I carry little pocket size flairs too, as well as a chemical light stick or two if all else fails. The chem stick is good for reading charts too without being too bright.
I don’t really use a flashlight. But it wouldn’t hurt to have one handy. We should indeed avoid shining it at other boats. But if one is bearing down on me appearing to not notice me you can bet I would make my presence known by any available means. As a last resort I would hit him with a flashlight.
those previously mentioned are good examples. I try to use USCG approved. And I strive for most reliable. Simple twist on/twist off LED is my preference.
I never assume the power boater can see me, is even watching, or is sober.