An addendum to my last post (given its own post here for the benefit of those of you who’ve already read it and moved in):
I am a bit embarrassed that I didn’t notice this at first, but these maps are very unkind to the millions of people with red-green colorblindness, as several commenters on the original OKTrends post mentioned. Here’s an approximation of what a red-green colorblind person sees when they look at one of those maps:

Run through http://colorfilter.wickline.org/ with protanopia filter
Designers cannot ignore such a vast population, and must take color vision anomalies into account.
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I don’t know if I’m colour blind or not but the colours on this map are easier for me to see than on the other one.