FYI Let me tell you the black cloth you are referring to is called is called Base and you what a base is it give structural strength okay so it does same by holding our hair under it and we tie our turban on it some time we use a strip of cloth of color of our choice on base to get our desired colors and over it we tie our turban (pagg), base helps in holding our hair so it can be a personal choice if you want to use it or not( if you can tie turban without it ), otherwise mostly we tie it up to keep our hair at place because we never cut our hair , and also I would like to tell you our gurus introduced us to pagg(turban) and in sikh religion we do not cut our hair, btw many people don't know Sikhism is not a religion its community and is called sikh comm. I hope I provided some valuable info to you