The most common and most likely answer to this crossword clue is the 7 letter word POLLOCK
I've seen this crossword clue in The Guardian
P
O
L
L
O
C
K
More clues leading to the result POLLOCK
Buddy explains!

The straight part
We know that "Painter" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case painter = pollock.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 POLLOCK mean?
POLLOCK noun- Either of two lean, white marine food fishes, of the genus Pollachius, in the cod family.
- To fish for pollock.
- To splatter, as with paint.