Hello, can my cocktail be blue? (10)
I believe the answer is:
melancholy
'be blue?' is the definition.
(thesaurus)
'hello can my cocktail' is the wordplay.
'cocktail' indicates an anagram.
'hello'+'can'+'my'='hellocanmy'
'hellocanmy' is an anagram of 'MELANCHOLY'.
(Other definitions for melancholy that I've seen before include "[ODE] subject" , "Gloomy, sad" , "Sadness, gloom" , "Sad - tendency to depression" , "Depressed" .)