Could I plot something like this below (scatter plot with gradual color response by a third variable) and add a fourth group variable identified by marker shape?
For example, there will be two groups, circles and triangles, each having graduated color scheme all on the same x-y plot.

scatter x=variable1 y=variable2 / colorresponse=variable3
markerattrs=(symbol=CircleFilled size=7)
colormodel=(CX3288BD CX99D594 CXE6F598 CXFEE08B CXFC8D59 CXD53E4F);