The default spectrogram command uses a single color and appears to just vary the saturation of the color to express intensity. So, for example, in the default implementation which looks like this:
its sort of a yellow which is darkened or lightened according to intensity.
I would rather have a bi-tone graphic in which there are two colors, say red and blue, and the intensity is continuous scale going from dark blue (low) to dark red (high). How can I do this?