What is the ruling on wearing the white skullcap, and is it a Sunnah?

Wearing a white or any other colored cap is permissible, with the exception of red, about which there is disagreement, unless it is specific to disbelievers, due to the Prophet’s (peace be upon him) saying: "Be different from the polytheists," and "Whoever imitates a people is one of them." What is specific to disbelievers varies according to time and place. It may be recommended to wear a skullcap upon entering the lavatory and during intercourse, to cover the head in these two situations.