Depth-cueing in RGB mode works in much the same way as in color map mode. The only difference is that a color ramp does not need to be loaded in the color map. Instead, the near and far RGB colors are specified, and intermediate points are colored by linearly interpolating between the near and far colors.
In general, the color map mode version of depth-cueing is more interesting and versatile, because one has direct control over the intermediate colors. For instance, every tenth color map entry can be made brilliant white, or deep black, to superimpose a depth grid on the figure.