In reply to Susan Durham.

Use the new HEATMAPDISC subroutine:
call heatmapdisc(R);
call heatmapdisc(X);
You can create and use your own sequential color ramp. The new PALETTE function is useful for a small number of categories. For more values, use linear interpolation to create a continuous color ramp, but use it with HEATMAPDISC.

I've recently blogged about the HEATMAPCONT subroutine and plan to blog on HEATMAPDISC in the next few months.