Malachite forms when copper minerals weather, and its banding records that process: each band is a growth episode, darker or lighter depending on the conditions. The pattern is a record of the stone's formation rather than a decoration on it.
One caution worth stating: malachite contains copper and the dust should not be inhaled. A polished bead worn against the skin is not a hazard, but this is not a material to grind or lap as a hobby. Natural banded material, not the reconstituted blocks that are also sold under this name.