Cockatiel droppings?

What color are they usually. i feed him harrisons diet and a basic seed diet. The seeds are blue, green, and brown.
His droppings are usually green. Not runny, just green and normal looking.
Yesterday, i think he ate some pieces of concrete when i took him outside.
He's been sleepy and grouchy all day.
I noticed black droppings that look like melted black plastic. It landed on his ladder and was hanging. I noticed some black and white droppings along with black to green ones.
Is he really sick?
Will it just pass through?
Can i do anything to help him?
Answers:
Birds will not normally eat non food items.
If his droppings have changed and hes lethargic Id suggest a trip to the Vet ASAP.
If hes sitting there all fluffed up and not eating .. somethings wrong birds often hide illness till its too late .. dont hesitate go to the vet!

---

Cockatiel droppings are round, not much wider than a #2 pencil eraser, green (waste)color in the outer band, white (urine) color inner band.
If he ate something bad it should pass through in 24 hours. If stool dropping are still off color take to see a vet A.S.A.P. who has a avian background.
For diet considerations, use natural seeds - not (food dye) colored seeds, pellets should be a part of their diet with seeds, and human food. My birds love angel hair pasta (cooked), Yellow American cheese, broccoli, yellow and white corn either kob or can and a produce aisle of fruits and veggies.