It's interesting to see this article on the front page at the same time as the Color Blindness article [1] discussing the difficulty of distinguishing tiny color spots. I'm not color blind, but I needed to zoom in on the first figure to see the difference between the red dot and the other red dot. Not to mention the black dot, the dark green dot that looks black at a distance, and the black dot that's actually an asterisk. Now I understand why these are so hard to distinguish.

[1] https://news.ycombinator.com/item?id=24672463