GReddy bov's
Neither of these are black. I have the Type R, and while it's not black, it behaves similar to what you describe.
Tial bov's come in several anodized colors, and the consensus seems to be that they don't open until 7psi or so. Perhaps this is what you have. They are unique in that they discharge in a 360 degree fashion.
tial bov
Hope this helps.
-john