The most common and most likely answer to this crossword clue is the 4 letter word PUCE
P
U
C
E
Buddy explains!

The straight part
We know that "Reddish-purple" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case reddish-purple = puce.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 PUCE mean?
PUCE noun- A brownish-purple color, sometimes more or less deep red or grayish.
- Of a brownish-purple color, sometimes more or less deep red or grayish.