There is a Dark Mode version of IconPong! MU has provided a special link to it above, marked "iconpong dark". Be sure to download it if you're using macOS 10.14 Mojave in Dark Mode! It works perfectly.
I use IconPong all day, every day to let me know if I have a working Internet connection. Between flakiness from my ISP, my occasionally temperamental cable modem and my aging Macs, I get cut off from the Internet about once a week. IconPong lets me know with an exclamation mark that there's no connection. Typically, turning WiFi off and on again on my Macs clears the problem. Thank you Alberto Roura!
Note that I've revised my review to 4 stars. iconPong is still awaiting user documentation. Meanwhile, here's an explanation from the developer's site on GitHub:
"What the icon dots mean:
"The icon is meant to be a domino, between 1-9 representing the ping time. That tells you at a quick glance whether ping times are ~<100ms or ~300ms or ~700ms or something greater (in which case it shows an exclamation mark)."