Franklinia need acidic moist well drained soils to do well. It could be chlorosis caused by the soil pH being to high. A photo would help.

Do you have rhododendrons or azaleas? How about Stewartia or Camellia?

Yup. There are two large rhodies, a large camellia, a hydrangea, and a Stewartia (pseudocamellia) within a few feet of the Franklinia. The Stewartia is behind the rhodies, so it isn't shown.

The other one isn't shown. It's in a different spot, with another rhodie, azalea, camellia, gardenia, and juniper.

Thanks.

Looks fine to me, just a young tree growing in a high temperature summer climate. Young sourwood look much the same, and attain a darker green as they grow larger and mature. As long as growth is good, keep watered in dry times and I think you will be okay. A close up of the foliage would be helpful.

just a young tree

Thanks. I was hoping that was all it was...

Here's my old tree today.

Here this year's seedlings in bark mix with slow releaseIn previous years have seen yellowing of new growth during hot/sultry weather which has not arrived yet for us. This is also influenced by rainfall which for us has been TOO MUCH of a good thing so far. What will happen to the foliage in July/August only time will tell.

hot/sultry weather

Hasn't been sultry here until the past few days, but unseasonably hot.

Good to know.