My Burning Bush ‘euonymus alatus’ is about 9 years old. Since I planted it, every year the leaves, both old and new, turn white never attained the deep green desired but do not turn brown, wither or drop. I Spring fertilize annually and keep the plant well-drained moist. The plant is mulched with 4-6″ of gravel. Whatever is the matter.
This does not sound like any of the common diseases (e.g., fungus, scale) that affect this species, which would likely result in the leaves falling off.
Have you considered testing your soil to measure the pH? The burning bush thrives in a slightly acidic soil. One reason is that when the soil is acidic, certain micronutrients, like iron, manganese, copper and zinc, are most available to the plant. If the soil is too alkaline, the shrub is prone to chlorosis, or yellowing of leaves, which is due to a lack of chlorophyll. Sometimes the leaves simply look pale and whitish.
Other causes of chlorosis include drainage problems, root damage or compaction and nutrient deficiencies (e.g., iron manganese, zinc). I’d suggest that you to take a leaf sample to your trusted nursery, and ask for information on the best products available to ensure the soil remains slightly acidic and to supply the micronutrients your plant might require.
You’re doing the right thing to keep the plant well-drained. However, mulching with an organic mulch or compost is preferred to gravel. These materials help create better soil conditions for the bush, for example, by acting as a source of nutrients.