Some fancy a nice greenish-blue colour (4)
I believe the answer is:
cyan
'greenish-blue colour' is the definition.
(I've seen this before)
'some fancy a nice' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'CYAN' is hidden in the letters of 'fancy a nice'.
(Other definitions for cyan that I've seen before include "Greeny blue" , "Greenish blue" , "Greenish-blue colour complementary to red" , "Bluish green" , "Blue printing ink" .)