Toenail regularly selected for greenish colour (4)
I believe the answer is:
teal
'greenish colour' is the definition.
'teal' can be an answer for 'colour' (teal is a kind of colour). I am not certain of the 'greenish' bit.
'toenail regularly selected' is the wordplay.
'regularly selected' indicates alternate letters (letters taken at regular intervals).
The alternating letters of 'toenail' are 'TEAL'.
'for' is the link.
Can you help me to learn more?
(Other definitions for teal that I've seen before include "Type of duck" , "Strange tale of a duck" , "Raise (subject matter)" , "Dark green-blue; duck" , "Small, short-necked duck" .)