Why might a single meteor streak exhibit a sequential color change, like yellow to green?

The meteoroid possesses layered or mixed mineral content that vaporizes sequentially.

The shift in color within a single, brief meteor streak indicates a complex and non-uniform chemical makeup within the original space rock. Meteoroids are rarely homogenous blocks of a single substance. As the object plunges deeper, increasing thermal energy ablates successive layers of material. If the outer layer is rich in an element like sodium (producing yellow/orange), and a subsequent layer contains magnesium (producing blue-green), the observer will see the color transition in sequence as the exposed material changes. This acts like a miniature, fast-moving fireworks display driven by the layered composition ignited at different ablation temperatures.