Here is one photo of the black leather interior, I believe I downloaded it from the Pontiac site?
If I had to describe it, I guess I would say the dash colors are in tones of black and off-black.
There are also a couple of shots of the black leather interior in the Gallery (see menu bar above) under the Solstice Interior Photos section. The gallery photos show the carpet better. (I have also attached one of the gallery photos, for those too lazy to hunt around for them.)
Again, I would call the carpet a dark grey or off-black rather than a true black.