Apparently, women in Japan are ashamed of their non-pink nipples. Because of the stigma surrounding this, they’re using creams to pinken their nipples.
And there’s a belief in Japan that pink nipples denote purity, while brown ones … don’t. A female plastic surgeon I know who works in Tokyo put it this way: “Japanese girls want to have pink nipples because Japanese guys like them. For some Japanese men, the less sexual experience a woman has, the better. Little experience means she is clean and precious for them.”
Like so many things from Japan, I found this quite strange. To put it both bluntly and crudely, however, I suppose someone from the country which invented the bleached asshole shouldn’t judge.