I want to point out that the console uses a (quite appealing [1]) fixed palette of 16 colors for all of its graphics. I think having a fixed palette is a great idea. I can see it helping would-be game developers overcome their initial art style analysis paralysis and helping ensure that the games have a recognizable "PICO-8" look.
You're right, it looks like much thought went into it. I se 4 distinct human skin tones, or 3 if you include a darker tone for shading, pleasant colors with darker tones for shading and good availability of high contrast (not everything is pastel).
[1] See http://i.imgur.com/1VOlxCt.png.