Ehehe, cool! I hope you don't mind that I deleted this post from Borhani's thread. It's totally cool, if you got it here!
Yeah, [m] is a toggle for brush blending modes, but it's only normal and additive thus far and highly experimental. I'll make a whole set of modes, soon! You gotta be careful with additive, because it's really just adding your selected color to what's on the canvas with every pixel all the time. That means you'll quickly blow out the color beyond 100%. I recommend using very, very dark colors and possibly low alpha...but you'll see.
Because it really just pumps the colors up, their power spreads naturally, if you smudge blown out colors around. That's kinda fun, because it makes such a hot spot like a repository for that color, hehe... but yeah... have fun with this experiment, but know that it's just temporary!