What Georgia snake is gray with a white belly?

The snake you are describing is likely the Eastern Rat Snake, also known as the black rat snake. While they are typically black, they can also be grayish, especially in certain regions or among younger individuals. This non-venomous snake is commonly found in Georgia and is known for its distinctive white or light-colored belly. Eastern Rat Snakes are often mistaken for other species but can be identified by their slender bodies and pattern variations.