Yellow vs. Blue

I think the blue ones are "new" as in, they were not in the popular section last week. They might have been last month or 2 weeks ago, but if they weren't last week, they get blue. I'm saying this comparing the rank of only 2 yellow and 2 blue ones, and although thsts what they indicate to be the coloring explanation, it's a fairly small number to be completely sure, so take this with a grain of doubt.