The most common and most likely answer to this crossword clue is the 9 letter word CHAMELEON
I've seen this crossword clue in The Times
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More clues leading to the result CHAMELEON
- Arrived carrying hotel sign with name, for colour changer
- One adapting to surroundings of clean home, transformed
- One to blend in drink with energy-packed fruit
- Tea and fruit taken round east of the Lizard?
- Beast of burden, one oddly biting head of harmless reptile
- Lizard in Ceylon, perhaps, existing on energy in fruit
- Unreliable character arrived carrying hotel sign with name
- Approached Trotsky outside hotel – such a cold-blooded customer!
- Changeable person smoked joint in church somewhere in Spain
- Fickle person taking tea with me before Christmas comes round
Buddy explains!

The straight part
We know that "One to blend in" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one to blend in = chameleon.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 CHAMELEON mean?
CHAMELEON noun- A small to mid-size reptile, of the family Chamaeleonidae, and one of the best known lizard families able to change color and project its long tongue.
- A person with inconstant behavior; one able to quickly adjust to new circumstances.
- A hypothetical scalar particle with a non-linear self-interaction, giving it an effective mass that depends on its environment: the presence of other fields.
- Describing something that changes color.