Is the practice of letting the end of the turban hang down the back of the head from the Sunnah or from custom, and is the recommendation of wearing white clothing among the customs-related Sunnahs pertaining to worldly matters?

It has been established that the Prophet, peace and blessings be upon him, wore a black turban and let its end hang between his hands. In another narration: "He let its two ends hang between his shoulders." He also wore all colors, but he preferred white, for he, peace and blessings be upon him, said: "Wear white from your clothes, for it is the best of your clothes, and shroud your dead in it." Some scholars have recommended wearing white and letting the end of the turban hang between the shoulders.