This layer is characteristic point of chrysanthemum. After burst, burning traler layer at first. Next burning each compound and changing color. A compound of this layer, leave cinders as visible trace. There are some kind of compound.
Typical powder is traditional black powder.
So after burst, appear each color without delay. These color compound layer not leave visible trace. Not, this pics show chrysanthemum with double pistil. This shell use chrysanthemum star in outer petal naturally. Probably, builder intend to show two pistils more clearly not hinder by outer main stars.