Saturday is dedicated to the fearful god Shani, who is one of the Navagrahas - or nine planets. He is represented as a deity carrying bow and arrows and riding a crow or a vulture.
There are temples exclusively dedicated to god Shani and normally they are painted black. The idol too is black in color, and sometimes made of iron. Devotees observing the Shanivar fast usually visit Shani shrines and offer black-colored items like sesame oil, black clothes, and black grams. After the evening prayers, those devotees take a single meal, which is usually cooked sans salt, prepared using sesame til or black gram or other black colored food items. Some worship the 'peepal tree' (the holy Indian fig) and tie thread around its bark. Shani is said to ward off ill effects, illness and troubles. Shani is so dreaded that many Hindus avoid long journeys on Saturday. Fast is observed by many to avoid the adversities and misfortunes on Shanivar. It is also believed that those who have Lord Hanuman's blessings are protected from Shani's wrath. So many people flock to Hanuman temple on Saturday.
Legend has it that Lord Hanuman had rescued Shani from Ravana, the demon king of Lanka, at the time when Hanuman set Lanka ablaze as depicted in the epic Ramayana. Lord Shani had then promised that he would not trouble Lord Hanuman devotees.
Color & Gem:
Blue and black are the preferred colors. Blue gems, such as, blue sapphire, black iron rings made of horse-shoe are worn to ward off Shani.