It's blue, because it scatters higher-energy light (from the sun) toward your eyes much more than it does lower-energy light. Blue light is high-energy (high frequency, low wavelength) and red is the opposite. This is the same reason the sky is blue (in the daytime, at least). :)

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灰色

不是啊，我是觉得不同地方的人对海寄托的情感不一样，他们眼中的海应该也是不一样的。所以想问一下(ฅ∀<`๑)

I think that any pleasant question in English, and that elicits answers in English, is fair game and appropriate to be asked here. Just my two cents. :)