The most common and most likely answer to this crossword clue is the 7 letter word NUANCES
I've seen this crossword clue in The Guardian
N
U
A
N
C
E
S
More clues leading to the result NUANCES
Buddy explains!

The straight part
We know that "s/ubtle differences" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case s/ubtle differences = nuances.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 NUANCES mean?
NUANCES noun- A minor distinction.
- Subtlety or fine detail.
- To apply a nuance to; to change or redefine in a subtle way.