Flowers are composed of modified leaves. Each floral structure represents a different modification of a leaf. You might think of a flower as a highly modified branch, the flower parts being highly modified leaves. The outer floral structure.
Most sepals are green, but they can be brightly colored like the petals.
Sepals protect the flower before blooming. All the sepals together are called the calyx . Usually brightly colored to attract pollinators. All the petals together are called the corolla . It is sticky so it can trap pollen grains.