Rationale behind topology_sample.png icon borders and colors?

[jlmuir]

Hello! Love the icon set! Love topology_sample.png too! I couldn't find your email address, and I couldn't find a way to ask a question, so I'm using an issue; quick question about topology_sample.png: What is the significance of, or your rationale for, using a square vs. a circle icon and a gray vs. blue icon? Thanks!