Now that we have seen how blue the sky really can be, we don't want to give it away.

既然我们已经领略了蔚蓝天空的模样，我们就不想让它逝去。

youdao

The blue of the sky paled to a light grey.

天空的蓝色渐变成了浅灰色。

《牛津词典》

Her silk shirt dress was sky-blue, the colour of her eyes.

她穿的真丝衬衫是天蓝色的，和她双眸的颜色一样。

《柯林斯英汉双解大词典》

This was because all you could see was the very blue sky and the very hot sun.

VOA: special.2009.01.14

Maybe it could refer to either the poet or the sun throughout the entire line, if you think of the mantle blue as being the actual sky that the sun is able to twitch over his shoulder.

或者两者皆可,从整句的行文看来，如果你们把蓝色的丝巾看作是真实的天空的话,那么太阳的确是能够在他的肩上轻轻颤动。

耶鲁公开课 - 弥尔顿课程节选

I think it was because people were overselling investments and saying, there's no limit to this investment but the blue sky above.

我想这是因为,当时人们过度宣传投资产品,并宣称,投资收益无止境,如头顶的蓝天那么遥远

耶鲁公开课 - 金融市场课程节选

Some 57 years later he wistfully remembered the regret at leaving the eternal snows of the Jungfrau and the sharp outline of the pyramid-shaped Silberhorn peak against the dark blue of the sky.

BBC: In Alpine villages, Hobbits lurk

"We are living in the lap of luxury here, " he said, gesturing to the blue sky and the magnificent city skyline.

BBC: Australia: Where the good life comes at a price

Cotopaxi, with its white cone brilliant against the blue sky, he found the most beautiful of all.

NPR: Excerpt: 'Natives and Exotics'