Blue celestial body close to Mercury (6)
I believe the answer is:
earthy
'blue' is the definition.
(both can mean sexual)
'celestial body close to mercury' is the wordplay.
'celestial body' becomes 'Earth' (Earth is an example).
'close to' says to take the final letters (the close/ending of).
The last letter of 'mercury' is 'y'.
'earth'+'y'='EARTHY'
(Other definitions for earthy that I've seen before include "Lusty, crude" , "Natural" , "Coarse, vulgar" , "Dirty" , "grubby" .)