Like a very dark maroon, but where the light highlights it you get a deep red/maroon. It's a very understated/sexy colour. I also think the same thing but with a blue hue instead of red would also be sexy.
I also agree ttoney in that, on these cars, it's more about shape than colour, and the dark colours hide the shape. I love 69 sportsroofs and whilst at uni one day I spotted one done in cool white with some nice shiny 17 inch chrome wheels. It was heavenly. White has other advantages - can be cheaper than other colours, no need to do it in a base/clear, it will keep the car cooler in the sun, it doesn't attract the wrong kind of attention (punks who think it is badass because it is black, and might damage it through jealousy, or cops who think you're a hoon because it is red...), and inversely to black, it looks pretty clean all the time.
Black (and dark shades) are all about the paint, you can see imperfections easily, dirt, scratches, warps, etc, but it's harder to see the shape, whereas white highlights the shape, and hides the surface imperfections.