The most common and most likely answer to this crossword clue is the 4 plus 4 plus 4 letter word BLUE WITH COLD
I've seen this crossword clue in The Daily Telegraph
B
L
U
E
W
I
T
H
C
O
L
D
Buddy explains!
The straight part
We know that "discoloured because of low temperature" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case discoloured because of low temperature = blue with cold.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.