Yellow variety of melon (5)
I believe the answer is:
lemon
'yellow' is the definition.
(lemon is a kind of yellow)
'variety of melon' is the wordplay.
'variety of' indicates an anagram.
'melon' is an anagram of 'LEMON'.
(Other definitions for lemon that I've seen before include "Dab" , "Melon is another fruit" , "Sharp-tasting fruit" , "Fruit squeezed on Pancake Day?" , "Fruit high in vitamin C" .)