Green is an amazingly easy color to paint. Maybe I am saying that because red so miserable to paint. It shades nicely with black and to make the highlight all you need to do is add a little white to your base color. It covers well even over a black undercoat.
Dark Angels present a specific problem of needing to paint dark, almost black, armor while still making it green and highlighting it. Dark Angel Green goes on ok over a black undercoat but it looks much better over a lighter one. Knarloc Green goes on great over a black coat and DAG looks great over that. After that you can give a sloppy highlight of Snott Green. A black wash darkens everything down and still retains depth and highlighting.
After this, less is more. the more you monkey with things, the worse it looks. Just a little Snott Green on the hard edges and the barest whisper of Goblin Green makes form awesome green armor.