I'm having a tough time getting my black saber to work...
In JO, I would have a negative grayscale lightsaber and I would use the blendFunc GL_DST_COLOR GL_SRC_COLOR in the shader. This worked, except for the fact that if you played JO in windowed mode, it would look really strange, seemingly displaying the white stuff instead of the black stuff.

In JA, I tried the same, but unfortunatly, it does the exact same thing as JO did in windowed mode... But ALL THE TIME!

As my black saber looks awful now, I'm just asking the GL blending pro's out there...

What is the correct blendFunc to use for displaying black lightsabers?

Right, to answer my own question then:

If you use a negative greyscale image of a lightsaber, and use the "blendFunc filter" in the shader, you can make it display a black lightsaber.

Good job. I'm working on a similar problem at the moment - got any pics of your black saber?