The most common and most likely answer to this crossword clue is the 4 letter word VERT
V
E
R
T
More clues leading to the result VERT
Buddy explains!

The straight part
We know that "green" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case green = vert.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 VERT mean?
VERT noun- A green colour, now only in heraldry; represented in engraving by diagonal parallel lines 45 degrees counter-clockwise.
- Green undergrowth or other vegetation growing in a forest, as a potential cover for deer.
- The right to fell trees or cut shrubs in a forest.
- In blazon, of the colour green.
- In sport, a type of bicycle stunt competition.
- A vertical surface used by skateboarders or skiers.
- Vertebrate