I didn't realise you could get them on other parts of your body, I thought they were always on your spine? If that's so, I think I have one on my left thigh.
Nai - that is what my kids have, both are dark patches on their thigh/hip and my Japanese MIL told me all kids with Japanese/Asian blood get them somewhere??? Otherwise maybe they are just a birth mark? Have googled and all I can find is the blue ones.