Yellowing baby pines
We had several baby pine trees in 1 gallon buckets that we transplanted this fall and they turned a yellowish color very soon after we planted them. I got them from Missouri conservation and they are native pine trees to our state. I want to say they are pineous conifers possibly. They grew great during the summer in the containers and looked very lush and green for fall trans-planting. Several that we planted in the ground in the spring of this year turned brown and died due to heat which is not that uncommon when growing Pines in Missouri.
Newton County Missouri trees and shrubs
If they are a native pine, they are most likely the short leaf pine which does really well here in Missouri. Give the pines until spring to see if they green up. You might consider getting a soil test and then fertilize in the spring based on the soil test results.