I was wondering what colors you would think could make this green?
Ok I'm not professional but to me he look's like he is almost lime green. Just a little darker. Why don't you use Americolor electric green to start. Then if you need to darken it. I would use a little leaf green. Good Luck!
As a color specialist, I agree with punkin90. Leaf Green or Forest Green will help darken the color. If the electric green looks too 'raw' you can tame it by adding a touch of it's compliment. The compliment of green is red, and since this shade of green has a lot of yellow in it, you could also add a touch of purple.
Try the slightest amount of red to start and add a touch more if necessary. The purple will help if the green starts looking too warm, or orangey. HTH