The pigment originally comes from the Italian region of Umbria, but the word ombra happens to mean shadow in Italian, and some people think that's the meaning of the color, because it's good for certain shadows. I don't recommend either of the umbers, because I find them too strong. You can obtain the same color by simply adding black, blue, or green to burnt, or raw sienna. It's very handy in aquarelle when you want to make other colors slightly darker, especially in the form of an over-all wash. Needless to say, grays of any shade can be obtained by adding more or less black to white, and modifying them with the addition of a touch of red, blue, green, or any other hue.
Ivory is anything but black.
The reason for the name is that this color is made of bone carbon, not necessarily from elephant tusk. It's transparent, so that it can be used as a wash or glaze when sufficiently diluted. Now I am aware of what purists say about black not being a color, and I know that in previous lessons I have counseled you to be cautious about using it. However, at this stage of our studies we ought to be accomplished artists with a keen awareness of how to handle our colors. Add a touch of burnt sienna to ivory black, and you have the identical black hue, but you obtain a considerably stronger paint.