I don't know what breed he is. The person you got him from was doing a school project? Would they know?
No, you don't need a Mom chicken, you could raise them all together outside in a coop/run.
Are you in the U.S.?
Cute little guy!
It's o.k., but it would be good to get him eating a nutritionally balanced poultry feed for most of his diet.
I would slowly start limiting the fruits/veggies, etc. But you'll have to work with him. He's learned if he doesn't eat his normal feed and...
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Can you please post photos of the poop and of your chicken?
How old is he?
What do you feed besides the fruits and veggies?
All those things you mention can certainly affect the color of the poop.
If you want to find out, then cut all those things out for a few days and just...