The most common and most likely answer to this crossword clue is the 8 letter word PASTIEST
P
A
S
T
I
E
S
T
Buddy explains!
The straight part
We know that "Most colourless" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most colourless = pastiest.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 PASTIEST mean?
PASTIEST adjective- Like paste, sticky.
- Pale, lacking colour, having a pallor
- White-skinned