The most common and most likely answer to this crossword clue is the 8 letter word CONTRAST
I've seen this crossword clue in The Sunday Telegraph
C
O
N
T
R
A
S
T
More clues leading to the result CONTRAST
Buddy explains!

The straight part
We know that "Difference" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case difference = contrast.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 CONTRAST mean?
CONTRAST noun- A difference in lightness, brightness and/or hue between two colours that makes them more or less distinguishable.
- A difference between two objects, people or concepts.
- Antithesis.
- To set in opposition in order to show the difference or differences between.
- To form a contrast.