You are a green card holder living in the US your parents are transferring 100000 to you to be used as part of a down payment on a home do you have to pay tax on this amount?

No, I really don't think so.

I'm not sure how it would be different than appearing to be your funds being used. If you went there and they gave it to you, and you used it here...even if you had them send it to you as they help with your affairs from there, it wouldn't be taxable income to you.

or alternatively, if they and you were here, and they gave it to you, as a family gift it wouldn't be income taxable to you, but something called "gift taxable" by them. However, I suspect that as non-citizens, this tax wouldn't apply to them either.