I did this last time where my customer requested a stackup of 2 bar graphs. Anyway, both my scenario and yours can be met by adding another plot of different color. Add another plot with blue colour and let it have value where you want the plot to be blue. Same goes for the green plot. To 'remove' the plots where they are 0, just set the value to NaN. In short, create two 1D array (1 is blue plot, 1 is green plot). Bundle each array with the x-axis array. Build the two clusters to an array before wiring them to the XY graph.