In this sentence, the superlative adjective "greyest" is incorrect because of the context of the sentence.
Usage of Adjectives:
Positive Degree ("grey"): Describes a quality without comparison.
Comparative Degree ("greyer"): Compares two things.
Superlative Degree ("greyest" or "most grey"): Compares three or more things.
Context: The sentence describes the state of the sky after a storm. It is not comparing the sky after this specific storm to the sky after multiple other storms to determine which one was the absolute "greyest."
Correct Usage: The simple positive adjective "grey" is the correct choice to describe the appearance of the sky in this context.
