Upon [horizontal] reflection
The center was my least favorite part of the entire quilt. I disliked how rough the set-of-three looked in comparison to the rest of the design.
When I went back to the original rendering of the tiling, I realized it had been colored more to show rings within rings. I immediately scrapped my old version for what you see here. It emphasizes the reflection symmetry (the left-hand side is the same as the right).
I also decided to emphasize the stars in the background, outside the inner ring.