I'm afraid that it will be difficult to answer this without seeing or knowing a great deal more about the planting site and conditions. These plants are quite specific about what they need to thrive in an environment and we have no way of knowing if you have supplied any of those conditions.

They must have a moist, but very well-drained site....preferably one where a great deal of organic matter has been mixed into the whole planting bed, not just the planting hole (which can be deadly). pH matters with Gardenia, as well. This has been a terribly dry winter in Northern Alabama, so monitoring soil moisture levels throughout the winter would have been very important, especially for newly planted material. Yet, if you are irrigating carelessly into the typical clay soils that are found in this location, over watering could be an issue.

What cold hardy variety of gardenia did you purchase?

1 gallon water, one tablespoon Epsom salts, fertilize with Miracid or an azalea fertilizer and add a dose of SuperThrive. See if that doesn't save it and make it green.

I plant mine fairly high in a mound of soil to which I add composted manure and/or finely ground pine mulch. Then I milch them with A LOT of pine bark mulch to keep them from drying out. They are pretty resilient once established. I see old, large Gardenias around here sitting out in pretty exposed places.