The answer, of course, is Sphinx Purple.
My first thought when I hear "Sphinx" is that big ol' fellow sitting out in Giza, which does such a good job of blending into the desert because it is sand-colored, not purple. But there are a wide variety of sphinxes in various cultural histories, and I am sure the nail polish namers have a very good reason for associating it with purple.
Now, the traditional portrayal of the Sphinx is a human head (some shade between peach and brown) on the body of a lion (golden). But in Egypt the head can sometimes also be a falcon's (brown, white, or gray), a hawk's (same), or a ram's (same plus black).
Hmm, no purple yet. Let's move onto other cultures. If we're going Greek, a sphinx can also have the wings of an eagle (black) and the tail of a serpent (green, yellow, red, brown, black, orange). And there's a Thai sphinx variant who might have the lower body of a deer (brown).
Still nothing? I could be looking at this too narrowly. Maybe we should consider the materials out of which a sphinx might be carved. They have been made out of all kinds of things, like limestone (sandy), granite (black, white, gray), and alabaster (uh...white).
That's it, I give up. There is a way to tie the concept of a sphinx to every conceivable color EXCEPT purple.
Wait! Wait, I've got it. The word sphinx comes from the Greek Σφίγξ, apparently from the verb σφίγγω (sphíngō), meaning "to strangle". (Thanks, Wikipedia!) So maybe this is the color that the Sphinx's victims turned after they failed at Elementary Riddles 101. Just what I always wanted to paint my nails.
