Conservationist of a sickly hue (5)
I believe the answer is:
green
This clue might be a double definition.
'conservationist' is the first definition.
(I've seen this before)
'a sickly hue' is the second definition.
'green' can be an answer for 'hue' (green is a kind of colour). I'm unsure of the 'a sickly' bit.
'of' is the link.
Can you help me to learn more?
(Other definitions for green that I've seen before include "Lacking experience (on the golf course?)" , "cheap marijuana" , "Environmentally sound" , "The colour of inexperience" , "Proverbial constituent of our moon" .)