How did you plant them? Did you soak the roots first in something like compost tea ("Garrett Juice") for a while then separate them and unwind them? I'm assuming these were in pots, not rootballs?
You had the right idea, planting them a bit high rather than too deep in the ground. Often trees that were grown in pots have had dirt dropped into the pot to make them look better at the nursery, and if they're in the pot long, adventitious roots grow into that dirt above the natural root line. Those can be removed, above the root flare.
If it has only been a week and one tree is turning yellow it could be a bit shocked, but if it doesn't improve, hopefully you bought them from someplace that has a return policy over a period of a few months (some nurseries will let you return plants within a year. Keep the pot and the receipt).
I'm sure someone who has a more detailed answer will come along and add to this. It sounds like you were doing it right, and sometimes these nursery plants just don't make it if they've been in the pot for a very long time.
Unfortunately I did not soak the roots in anything before planting; you are correct they were potted plants. I wasn't told about doing this at Home Depot when I bought the "Natures Helper" mix. I probably should have been notified about it because I would've done so if it was mentioned. I did my best to separate the roots but they were so small I was somewhat afraid I was going to break them. I bought the trees from Costco and I have already inquired about the return policy. They stated that I could get a replacement tree if I still had a receipt for up to a year after the purchase date and that I didn't even have to bring the tree back in. I asked my aunt who studied horticulture and she did say that the tree could be shocked and/or it could have been overwatered. With the soil concentration here being primarily clay, she told me to lay off the water for a while and see if it improved. I've attached two pics of the 'yellowing' tree below and two pics of the other two healthy trees.