I made an edit.
If you look at references, you will notice his hair isn't typically depicted to be that long and the robe is usually not just one piece of white.
You might also want to clean up those thick black lines and make use of all the intermediates on the robe for a little less heavy handed definition altho I didn't manage to pull it off quite as well as others around here can so take it with a grain of salt.
Your tones are also a bit close to each other, the dark green is barely distinguishable from the black so more contrast between those tones would be helpful if you want people to actually see the work you put into the black and dark green clusters.