This is the bottom of the cast as it is displayed. Because the cast is displayed upside down from the natural orientation, this is the part of the colony closest to the ground surface.
You should be able to see three small paint marks on the cast. A red dot on the right, blue on the left, and black near the top of the cast. These marks correspond to paint marks on the three base support risers
and are there to help align the cast on the base in the proper position.