Lime can turn shrimp pink because it is a natural food dye. The lime juice will change the color of the shrimp's flesh as it cooks. The shrimp will first turn pink around the edges, then turn ghostly translucent, then appear cooked. The color of shrimp is affected by a number of factors, including the pH level of the water, the presence of certain chemicals, and the temperature of the water. In general, shrimp will turn pink when they are cooked, but the process of cooking them also causes them to lose their natural color.