Why do leopard frogs come in two colors?

The persistence of two colors everywhere suggests a balance of evolutionary forces

Northern Leopard Frog

Leopard frog - Wikipedia

Hinterland Who's Who - Northern Leopard Frog

Northern Leopard Frog

Minnesota Seasons - northern leopard frog

Lithobates pipiens – Northern Leopard Frog

Northern Leopard Frog, Rana pipiens pipiens

Northern Leopard Frog

Northern leopard frog have fewer places to sing, meet and breed tadpoles from a 6,000-egg jelly - Cambridge Day

Natural Selections: Why do leopard frogs come in two colors?