My '87 has a bit of fine metallic in the factory finish. Guessing it's in the clearcoat but don't know for sure. I'd run the question by some good painters: Joe Bell, Keith Anderson, Allan Wanta, CycleArt, etc.
Interested in what you find out. I have a 3.0 MTB frameset that I need to get painted. It's going to be a reproduction of my stolen 1989 SM800, which came with pretty much the same paint and decals as the Black Lightning. Interesting that the 1989 catalog lists the Black Lightning color as Ebony and the SM800 as black. The 1987 Black Lightning was listed as black, don't know if the paint changed over the years or not.
You might want to try 2008-2009 Jeep Patriot black touchup paint. When I looked at one at the dealership it had a slight silver flake in it. While I could not directly compare it to my 1988 Black Lightning it appeared to be a good match. Like the original Cannondale paint the effect is subtle until you look closely.