I can't believe this.

Most Asian babies have blue marks on their rear-ends and lower backs called moukohan. Known as Mongolian Spots in English, they are a dense collection of Melanin-containing cells called Melanocytes. Melanin is the chemical which gives our skin its colour, and if the melanocytes are deep under the skin, they appear blue. The spots generally fade within a few years and almost always disappear by puberty. These spots have given rise to an interesting Japanese idiom, "shiri ga aoi". It means "his butt is blue" and is used to describe a person that is childish or inexperienced.

--Japanese SAQ (Seldom Asked Questions)

Who woulda thunk that babies being born all over the place with blue bottoms would have escaped my realm of knowledge. Sheez. Apparently, about 90% of children of pigmented-skin races have these Mongolian spots (www.chinaconnectiononline.com/mongspot.htm).

Visit the site I referenced above for all kinds of weird information about japanese people. I'll have to ask my coworkers about this blue baby bottom business.