I need to study it more, but I know that it can change colors, I am not sure if it depends on the sprite the particle uses, or if that is simply ignored. It uses a mixture of the white color and black color settings to control the colors.
I am not sure if the lighting value itself can be brighter or darker and I need to test more.
I don't think negative values could work, and there is no directional lighting at all, as it covers the entire world space.
I also don't think it fades in/out smoothly. I suspect this same color/lighting system was used for the spiritual invincibility, which DOES smoothly transition.
So yeah, a lot more testing is required, I'll test out some of your direct questions and see how it goes.