Everyone's favorite not-quite-making-it-big-in-the-U.S. idol UTADA Hikaru is about to release her fourth solo Japanese-language solo album (but sixth album overall), ULTRA BLUE. In the June 5th edition of the free Tower Records sales-chasing mini-magazine, she discusses the title:

なんか＜青＞っていうのがすごいキーワードだなって思ったのね。青って青春の青だったり、希望があって若くて…でも、ブルーには謎めいた部分もあって。それでいて受け入れる色って感じもして。それがすごく今の自分だなぁと思った。

It's like, I just thought that "ao" was totally a keyword. It's the sei in seishun, when you're young and full of dreams... but "blue" has this enigmatic side to it, too. Like, the color of just accepting things. And I thought, that's totally me right now.

Ao is a native Japanese word for "blue/green" (think: the color of the sea, the sky, young leaves), written with the Chinese character 青, which is also sometimes used to write the Chinese-derived morpheme of roughly the same meaning, sei, instead. Seishun literally means "blue/green spring" and figuratively refers to the time when you are, well, young and full of hopes and dreams. (It starts sometime after you enter junior high or high school and ends either during or when you graduate from university, I believe.) Your salad days, when you are still... green.

See, the problem is that ao is an example of the very common phenomenon whereby color words don't quite map perfectly from one language to the other. If you say that ao is blue, you're saying that in Japan, you step on the gas when the light turns blue. If you say, okay, I guess ao is green, you're arguing for a green sky over East Asia.

(An interesting Wenbudao post a while ago suggested that the reason it pulls this double duty in Japanese but not in English, etc., is because Japanese only has four native color adjectives, and the first three are reserved for white, black and red. ["But what about midori?" (the other word for green), I hear you cry. That was originally a noun referring to new plant growth, and only became used as a color word later on.])

In summary, ao or 青 might be useful for implying youthfulness, but as a native English speaker I don't think that "BLUE" is.

However, having said all that, Utada has lived much of her life in New York and her English is reportedly very good -- some dare call her a native speaker. I don't think she is unaware of this issue. She's just playing to her audience: Japanese speakers. When they first learn colors, ao generally gets assigned to "blue", and not many of them care enough to get to the point where they learn that sometimes it's "green" instead. She is using the English of Japan rather than of New York to make her point.

That, or I'm reading way too much into some line she spun out desperately while trying to think of an interesting soundbite about the album.