The most common and most likely answer to this crossword clue is the 2 plus 4 plus 2 plus 7 letter word AS KEEN AS MUSTARD
I've seen this crossword clue in The Guardian
A
S
K
E
E
N
A
S
M
U
S
T
A
R
D
More clues leading to the result AS KEEN AS MUSTARD
Buddy explains!
The straight part
We know that "Enthusiastic, by Colman’s standard" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case enthusiastic, by colman’s standard = as keen as mustard.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.