Blue Planet back on telly (6)
I believe the answer is:
earthy
'blue' is the definition.
(both can mean sexual)
'planet back on telly' is the wordplay.
'planet' becomes 'earth' (Earth is an example).
'back on' says to take the final letters (the letter at the back).
The final letter of 'telly' is 'y'.
'earth'+'y'='EARTHY'
(Other definitions for earthy that I've seen before include "Unenthusiastic" , "Like soil; uninhibitedly direct" , "Coarse as humour may be" , "Dirty" , "Gross, like the soil" .)