The most common and most likely answer to this crossword clue is the 9 letter word TURQUOISE
I've seen this crossword clue in The Guardian
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More clues leading to the result TURQUOISE
- Quite sour nuts, greenish-blue
- Corrupt squire out to get semiprecious stone
- A shade sour and quite foul
- Our quiet’s disturbed, making us sort of blue
- Quite sour cocktail is a shade of blue
- Quite sour, off colour
- Quite sour, distressed and blue
- Quarterback in France about two miles out, in the shade?
- Quite sour, out of sorts, somewhat blue?
- Our quest’s ridiculous, touring Italy for gemstone
Buddy explains!

The straight part
We know that "colour" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case colour = turquoise.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TURQUOISE mean?
TURQUOISE noun- A sky-blue, greenish-blue, or greenish-gray semi-precious gemstone.
- A pale greenish-blue colour, like that of the gemstone.
- Made of turquoise (the gemstone).
- Having a pale greenish-blue colour.