You can also find black cocoa relatively easy these days. Most cake decorating stores and supply stores like Penzey's carry it. It will yield the darkest chocolate color. As someone mentioned Dutch Processed cocoas tend to yield a darker product but in large quantities it might not taste the same if the recipe calls for standard cocoa. In smaller quantities it won't matter much but if it calls for a lot, you might want to look for recipes that specifically ask for a Dutch processed type. Good luck!
I was wondering if anyone knows how to make really dark chocolate cake -- and I don't mean necessarily the flavor (as in bitter). I have seen some cakes that are dark in color, almost close to black (as in devil's food cake).
Is it because of the ingredients or the way it was cooked? I would like to learn how to make this.