This picture shows the base detail. They are similar, but a close examination reveals some differences. The purple one has four tiny "dots" on the inner skirts, spaced equally around the circumference. These appear to be air vents to aid in the proper molding. The inner skirts are otherwise very smoothly finished. Indeed, the entire surface of the purple one is very smooth and very nicely finished.

The aqua one has a mold seam that runs around the entire bottom of each inner skirt, and although it has a few irregularities in this line, it does not show obvious equally spaced vents. The surface is also noticeably cruder, with more distortions from manufacturing and mold surface irregularities in general.