Sorry I forgot to respond! I meant to follow up by looking it up in Berlin & Kay's World Color Survey, then forgot, then realized that the WCS doesn't have that information. :| I *think* it's both lightness and hue, but I don't know for sure.

I've had Japanese students who've used Kuriki et al's work on Japanese color terms in their research and generally agreed with the paper's "definitions" of the focal colors; here's a link to that: jov.arvojournals.org/article.aspx...