The most common and most likely answer to this crossword clue is the 13 letter word POSTERÂ PAINTS
P
O
S
T
E
R
Â
P
A
I
N
T
S
Buddy explains!
The straight part
We know that "Range of bright colours" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case range of bright colours = poster paints.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.