Why Cerebrum upper surface is gray but spinal chord upper surface is white?

The upper surface of the cerebrum appears gray due to the presence of neuronal cell bodies, which are concentrated in the cerebral cortex, giving it a gray color known as gray matter. In contrast, the spinal cord's upper surface appears white because it primarily contains myelinated axons, which are part of the white matter. The myelin sheaths around these axons provide insulation and facilitate faster signal transmission, resulting in the white appearance. This structural differentiation reflects the distinct functions of these brain and spinal cord regions in processing and transmitting information.