The most common and most likely answer to this crossword clue is the 5 letter word STRAW
I've seen this crossword clue in The Times
S
T
R
A
W
More clues leading to the result STRAW
- A feature on Cromwell rejected as corny stuff
- Sucker with no science subjects upset
- Criminal coward rues lot, being yellow as old grass
- Unsightly growths set back remains of crop
- Means to absorb paintings etc back in Cornwall area
- Fast-food freebie recalled, growths found on skin
- Thatcher is closely associated with thisĀ former Cabinet minister
- Way to get untreated stable bed?
- Yellowish-brown lumps rejected
- Recall lumps in trifle
Buddy explains!

The straight part
We know that "yellow as old grass" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case yellow as old grass = straw.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 STRAW mean?
STRAW noun- A dried stalk of a cereal plant.
- Such dried stalks considered collectively.
- A drinking straw.
- A pale, yellowish beige colour, like that of a dried straw.
- Anything proverbially worthless; the least possible thing.
- To lay straw around plants to protect them from frost.
- To sell straws on the streets in order to cover the giving to the purchaser of things usually banned, such as pornography.
- Made of straw.
- Of a pale, yellowish beige colour, like that of a dried straw.
- Imaginary, but presented as real.