GR translation: shaken skies pure as a cyclorama

[Mike Jing]

The moment the comb contacts his head, the colonel begins to speak.
“Ordinarily, we’d spend no more than 24 hours on a house-to-house sweep.
Sundown to sundown, house to house. There’s a quality of black and gold to
either end of it, that way, silhouettes, shaken skies pure as a cyclorama.
But these sunsets, out here, I don’t know. Do you suppose something has
exploded somewhere? Really—somewhere in the East? Another Krakatoa? Another
name at least that exotic . . the colors are so different now. Volcanic
ash, or any finely-divided substance, suspended in the atmosphere, can
diffract the colors strangely. Did you know that, son? Hard to believe,
isn’t it?

What does "shaken" indicate here?
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