Coarse show includes blue material ultimately (10)
I believe the answer is:
indelicate
'coarse' is the definition.
(thesaurus)
'show includes blue material ultimately' is the wordplay.
'show' becomes 'indicate' ('indicate' can be a synonym of 'show'**).
'includes' is an insertion indicator.
'ultimately' says to take the final letters.
The last letters of 'blue material' are 'el'.
'indicate' enclosing 'el' is 'INDELICATE'.
(Other definitions for indelicate that I've seen before include "Rude - tasteless" , "Practised (a play)" , "Rather rude" , "lacking taste" , "Saucy" .)