The magnesium riser TD's came in a variety of colors-black, brown, white, green, blue, and yellow all come to mind. I believe the earliest risers actually had a 'flocked' or textured-type finish on them. The last year they were produced the finish was called metal-vein(if I recall correctly).
I have used regular sand paper and a dremel tool with a small wire brush attachment to remove old paint from the riser. I never like messing with chemical strippers if I can avoid it.
I have used regular Krylon/Rustoleum to repaint risers. It works ok but is not as durable as the original paint.
I had a friend that had his riser powder-coated and he liked it pretty well. I had also considered sending a riser out and having it film-dipped in a camo pattern. Hpoe this helps, good luck.