Cowpeas, often known as black-eyed peas, can exhibit variations in pigmentation due to the presence of anthocyanin pigments. These pigments are responsible for the black or purple "eye" on some cowpea varieties. Anthocyanins are natural pigments found in many plants, including some varieties of cowpeas. They can produce a range of colors, including red, purple, and blue, depending on the pH level of the environment. In the case of cowpeas, they contribute to the pigmentation of the "eye" or spot on the bean. The concentration of anthocyanin pigments in cowpeas can vary based on factors like genetics and growing conditions. Some cowpea varieties naturally have a higher concentration of these pigments, resulting in a more pronounced black or purple "eye."
When you cook cowpeas, especially those with a higher concentration of anthocyanins, the pigments may leach into the cooking water. This can impart a gray or purple tint to the water and sometimes to the beans themselves, although the beans may still have a dominant white or beige color.