Just read and interesting science article about how Humans are actually Bioluminescent but we can't see it because our eyes are not sensitive enough.
How amazing would that look to aliens? Especially if it were different colours like the Naa'vi in Avatar -- Adam in Darwin
The most astonishing fact that the Scollarids learned about Humans was this: Humans can't see their own glow. These Deathworlders were on par with them when it came to surviving strategies. They did more with less, did less with more, and got into further territories than any other species known to intelligent life. It seemed like they could - as a species - accomplish anything.
But they could not see how their colours wavered and intermixed with their moods. They couldn't perceive the soft, warm tones of their own body heat, or the subtle patterns of their inner radiations as they went through their days. The Scollarids said, Humans are beautiful in the dark, and the Humans didn't understand it as a compliment.
Humans glow. Their soft illumination has soothed many an infant Scollarid in the middle of the night. Their mood-lamp patterns of infra-red, ultra-violet, and electron blue have calmed hundreds in times of stress. It's such a pity that they can't see themselves with Scollarid eyes.