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Early color changes can be a sign of stress.

Spider Mite infestation is one possible cause.
Heat stress can also cause leaf color change, this is often the case when the bush gets more heat from a planting near a sidewalk or driveway or is getting reflection from a building.

Mechanical damage from mowers or weed wackers could also stress your plant.

https://www.gardeningknowhow.com/ornamental/shrubs/burning-bush/burning-bush-care.htm

Deer may avoid a Burning Bush, though if hungry they will eat them.

Shrubs and trees generally spend their first year in the ground establishing their roots. So while you may not see much above ground growth, there is likely lots of below ground growth. Which is what you want. A healthy root system will ensure long lived plants.

But don't worry, in a few months they will change their focus to above ground growth and they will just take off.

The dwarf version of burning bush naturally grows to 8-10 feet. It is a fast grower if given enough sun to produce red fall leaves. I don't think you'll be happy with the results of your plan and I think the plant will suffer as well. This is my opinion, you understand. A better choices are lavender, Little Henry sweetspire, blue mist flower (Caryopteris), compact hybrids of spirea and butterfly bush and catmint (Nepeta).

Here is an article that helps explain why plant leaves turn yellow: https://www.gardeningknowhow.com/plant-problems/environmental/plant-leaves-turn-yellow.htm

In general, burning bush, Euonymus alatus, does not need fertilization. It is also late in the year, depending on where you live. Fertilizing tells the plant to grow right when it should be shifting to hardening off for winter. The result of late fertilizing is growth that might succumb to winter kill. If you want to fertilize in spring, any general shrub fertilizer will do. I would not use a high nitrogen product.