Actually cyano comes in a multitude of colors and the aforemost authority on cyano would be Mr. TDWyatt. And Buzz it does come in a nice shade of blackish green. I have have the red velvet and the blackish green when my tank started up and I still occasionally get the velvet red. Hope that answers your question and hopefully TDWyatt will chime in.
Actually TDWyatt has a really cool presentation on cyano and the different changes and stages a tank goes through along with the dread algal blooms. If he gets on he has some really good insight on the prehistoric bacteria that multiplies like crazy and is an intregal part of the healthy balance of our tanks and our world's ocean.
Hey guys, I will post tomorrow or tomorrow nite, just too late getting in tonight (from the REAL job... ), been out in the workshop trying to get everything ready for next week when the rock goes into the new tanks... ... finished the cabinetry and working on the plumbing... ... : Lights should be ready after the stuff goes into the tanks. Check out the archives for threads, I think Andy Daiss of the ARC has the outline from the Atlanta presentation posted somewhere, but there are several good threads posted by several folks in the archives as well.
And yes, Cyanobacteria does come in a bright green mass as well as black, brown, red, bluegreen, and even a yellow spp. based on whatever accessory pigments are present in the particular spp. in your system. They all respond to the same means of limitation and control, although there are a few species that have the capability to fix nitrogen from the atmosphere (heh, hope this is NOT what is in your tank)