Musings on Fast Company Design’s design

I put up this question on Quora a couple of days ago, no answers yet: what do the different-coloured bars in the archive section of Fast Company Design’s blog refer to? Is there any logic to it or is it, as it seems to me now, random? I had various guesses but they don’t seem right: one, that a particular colour refers to a specific date in a month (so pink = the 1st of the month, blue = 4th and so on), but that’s clearly not right. Then I thought it was just a different shade each day, but nope, some colours repeat and some (dark blue) don’t.