The most common and most likely answer to this crossword clue is the 4 plus 3 plus 6 letter word SALT AND PEPPER
I've seen this crossword clue in The Guardian
S
A
L
T
A
N
D
P
E
P
P
E
R
Buddy explains!
The straight part
We know that "shades of light and dark" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shades of light and dark = salt and pepper.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 SALT AND PEPPER mean?
SALT AND PEPPER adjective- Having a color pattern resembling many small speckles of black and white.