The most common and most likely answer to this crossword clue is the 7 letter word JONQUIL
I've seen this crossword clue in The Times
J
O
N
Q
U
I
L
Buddy explains!

The straight part
We know that "a bloomer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a bloomer = jonquil.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 JONQUIL mean?
JONQUIL noun- A fragrant bulb flower (Narcissus jonquilla), a species of daffodil.
- A shade of yellow.