The most common and most likely answer to this crossword clue is the 8 plus 6 letter word PAVEMENT ARTIST
I've seen this crossword clue in The Sunday Telegraph
P
A
V
E
M
E
N
T
A
R
T
I
S
T
More clues leading to the result PAVEMENT ARTIST
Buddy explains!
The straight part
We know that "Might one paint colours on flag?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case might one paint colours on flag? = pavement artist.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.