Some fancy a new colour (4)
I believe the answer is:
cyan
'colour' is the definition.
(greenish blue colour)
'some fancy a new' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'CYAN' can be found hidden inside 'fancy a new'.
(Other definitions for cyan that I've seen before include "Primary subtractive colour" , "Greenish blue" , "Printer's blue" , "Primary blue colour in printing" , "Bluish-green" .)