As you can tell from the first two swatches, the base jelly color is different, the glitter is the same. Chunky Holo Black is a bit different. It has larger hexagonal glitter particles in the mix. These hexagonal flakes have the same holographic effect as the rest of the glitter. I’m guessing this is the particular color that was getting the buzz.
So to answer the question from the first post. Which two polishes to get for layering? Chunky Holo Black and any other one that catches your fancy. Sans the Black, you’ll pretty much get the same effect.