Purps, less commonly known as Homo Sapiens Purpureum, are a human sub-species, and are the result of a half-finished (one might say "half-baked") attempt to modify human stock to be more energy efficient. Eight hundred years after the original project was terminated, they still breed true, but are only a tiny bit more energy-efficient than their cousins, and then only when standing stark naked in direct sunlight.
The extra chromosomes they carry make cross-breeding between purps and standard humans less than successful: the resulting infant is blue, not because of photosynthetic skin, but because it is dead. For this reason, when Momma tells you "don't go marryin' one o' them purps", it's not because purps are inherently bad people, or because your Momma is a bigoted, buck-toothed racist. It's because Momma wants to be a grandma. I'm sure that purp girl you met is very nice, but if you two want to start a family, you're going to need to hire an adoption agent, a good geneticist, a marriage counselor, and maybe even a personal trainer.
Their photosynthetic skin creates energy for their bodies from light 2003-03-11. This leads some purps to shun sunlight, or at the very least, cover up really well.
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