Slicing for MMU3 not respecting multimaterial painting designations  

Slicing for MMU3 not respecting multimaterial painting designations

Hi All!

The .3mf file for this question can be downloaded from Google Drive.

I am setting up a multimaterial print, and I have used the Prusa Slicer multimaterial painting tool to apply my desired colors to the model (see first image). When I slice this design, the desired white background is assigned to green (see second image). NB, the bottom of the print (i.e. first layer) should be green.

My first guess was that this was something to do with the number of layers in the base plate, but there are 6 layers before the surface that is supposed to be white, plenty for a transition from green (the underside) to white.

What really confuses me is that when I attempt to fill the background with a different color (see third image), the slicer seems to respect the desired color (see fourth image). 

Finally, if I try coloring the part that should be white with a color that is not present anywhere else in my design (violet), the painted color is, once again, not respected (see images five and six).

So this makes me think that there is something about having contiguous colors (like the orange and black) that helps the slicer respect the requested color? Honestly, I am quite puzzled. Any help or ideas you might have would be greatly appreciated.