A greenish-yellow colour, but endlessly eloquent in a party (7)
I believe the answer is:
avocado
'a greenish-yellow colour' is the definition.
(avocado is a shade of green)
'but endlessly eloquent in a party' is the wordplay.
'but endlessly' means to remove the last letter.
'eloquent' becomes 'vocal' (eloquent means speaking fluently).
'in' is an insertion indicator.
'party' becomes 'do' (do is a kind of party).
'vocal' with its last letter taken away is 'voca'.
'a'+'do'='ado'
'voca' inserted within 'ado' is 'AVOCADO'.
(Other definitions for avocado that I've seen before include "Green-fleshed fruit" , "Light green colour" , "A dark green pear with cramy flesh" , "may be stoned" , "Shade of green" .)