do you know if there is a limit on how many colors can be displayed in a single palette? I'm trying to use 200 colors but the plot assigns wrong colors to each unit...

There's no practical limit, so 200 is fine. Are the colors wrong in the basic renderer or the raytraced renderer? For the former, you need to have the correct color array, min color and max color set for the StackTreeMap layout update function. For the latter, you need to create the equivalent 200 materials and material ids to map each data row to the corresponding material.