Black is a challenging color in watercolor, at least for me. Most tube blacks in my experience are dull and flat out of the tube. Ivory black I have found useful when mixed with other pigments, such as payne's gray when I need to develop a painting quickly.
However, I have come upon a new combination of ultramarine blue with burnt sienna and alizarin crimson. This makes a lively black wth some variation of dark tones.
You can see this combination in the above watercolor study I painted recently. This picture has one wash and it reads as one variation of black except for the white of the paper.
