Hi Robin,

This may be river birch "Shiloh Splash," which has variegated leaves. The variegation is more exaggerated in the sun.

This tree can revert to having green leaves on branches as it matures. Those branches are supposed to be pruned off. I think this is what happened to your tree.

https://mcilab.ces.ncsu.edu/plant-introductions/shiloh-splash-river-birch/

If most of the tree has green leaves it's too late to correct this through pruning. If there are only a few green branches, pruning is best done in late summer or in the fall, when the trees will lose less sap. You should never remove more than an third of the canopy at once, and less is better for the health of the tree.

Good luck.