Cup turned European colour (4)
I believe the answer is:
puce
'colour' is the definition.
(I know that puce is a colour)
'cup turned european' is the wordplay.
'turned' says the letters should be written in reverse.
'european' becomes 'e' (abbreviation e.g. EU).
'cup' back-to-front is 'puc'.
'puc'+'e'='PUCE'
(Other definitions for puce that I've seen before include "Deep red to brownish purple" , "Shade" , "Purplish colour" , "Pinkish purple" , "Brownish-purple colour" .)