You can't. MATLAB offers those string options for colors. If you want to set a specific color, you can, but as a numeric vector of length 3. You need to provide RGB code values.
For example, for a purple of sorts, you might do this:
H = surf(rand(10));
H.FaceColor = [.5 0 .5];
Not my favorite color scheme, but it is purple. And, for an olive, you might try something like this:
H.FaceColor = [.3 .4 .2];
You get the idea.
