Last year I enquired during the factory tour at DCC about a jet black Diamond. They can do it with paint, but not with Dymaondwood rails. The manufacturer of Dyamondwood can't make them jet black, and Diamond has asked them in the past for jet black. They are more like black with grey streaks in it.
Also, the standard Diamond wood is oak (real wood). If you wanted that jet black, you would still be able to see the cathedral oak grain through the color. Best bet is to choose maple or birch for the table instead of oak, then have them paint that jet black. Those two woods are closed pore woods, and smooth grain. They are excellent for painting in a solid color, because the grain does not show through.