The reason for that color shift was murky-perhaps for UV protection or camouflage.

颜色变化的原因尚不明朗，也许是为了防紫外线或伪装。

This natural color shift, combined with the decreasing brightness, tells our body to kick start the production of melatonin, which makes us feel sleepy.

这种自然的色温变化，加上亮度的下降，会告诉我们的身体开始生产褪黑激素，使我们感到困倦。

It's usually easy to see if someone painted an image in grayscale first, because the saturation of the color shifts will always feel a bit off.

通常很容易看出是否有人先以灰度绘制图像，因为颜色变化的饱和度总是会让人感觉有点偏差。