You need a bit more of the context to fully understand. I can't seem to copy and paste from Google books, so
here's the link. Relevant text begins on page 463, 2nd paragraph.
The story is about two women, one the wife and other a mistress the husband has taken. The sentence in question is part of an explanation (from the wife who's narrating) that both women know that within every woman hides a prostitute, and within every prostitute hides a lady. (author's words, not mine!)
The sentence you ask about states that the former is obvious because while a woman may act demure with her downcast gaze looking up through her lashes, at the same time she's hiding libidinous urges underneath her skirt.
At one point in history, a prim, proper, and polite woman would not have directly met the gaze of a man who wasn't her husband (or immediate blood relative). That's the lady bit. The bit about "swarming blue-green lights" seem to just be a euphemism for sexual urges.
There may some reference that I'm missing that would associate the colors with sexual urges. It's worth noting that this is a translation from the original Spanish, so there might be some cultural reference in there as well that I'm missing. Also, while this English translation uses 'prostitute', I suspect a more accurate term might be 'slut'.
I'm trying to find the original Spanish version and see what word for the mistress is used.
update: I found a copy of the original Spanish story
here. It does use the word 'prostituta' in Spanish. However, the English version of 'blue-green lights beneath her skirts' has been softened a bit with euphemisms, as the Spanish version says "verdes y azules en el fondo de sus v*ginas"
I had to have a native Spanish speaking colleague help me with this, and she didn't get the blue-green lights either. However, she's from Mexico, and the author was Puerto Rican, so it could be something dialectical.
