Color Transparency in a 3d scatter plot as a function

I'm trying to plot several different types of data in a 3d scatter plot with the color transparency as a function of the z axis. For a visual, let the color of set1=blue and the color of set2=red. As the data in set 1 goes up in the z-axis, the transparency goes down and turns more blue. as the data in set 2 goes up in the z-axis, the transparency goes down and turns more red.

I've been able to produce a code that has a color scale based on the z-axis, but doing so doesn't allow for the difference in data sets to be displayed. Having Transparency as a function of the z-axis would allow the different data sets to be plotted in the same graph and have a color based on the z axis.

Any suggestions?