The white part of the poop is normal. Green poo can be caused by them eating a lot of green grass and things. If it's bright green, that's a concern. You've done the best you can for him for tonight. Give him as much water as he will take. If you have chick vitamins, you could add that too...
Can you give some more information about him? How old he is and any other info about how he has been kept. Are there any other symptoms? Has he ever been sick before?
Green poo can be a sign of starvation. There are many things that can cause the starvation. He needs supportive care while...