Sri Swami Vishwananda talks about the eighth form of Maa called Mahagauri Devi.....

 The Divine Mother's eighth form is known as Mahagauri. Her complexion is totally white. Her garments are also white. White symbolises the purity of the true Self which is without any stain or impurity. She is mounted on an ox and has four arms.  Parvati had turned dark after doing intense penance for obtaining Lord Shiva as her husband. Shiva then bathed Her in the Holy Ganges, She turned fair and became known as Mahagauri.  Due to the Mother’s Grace the devotee crosses the barrier of limitation and attains supernatural salvation. He is relieved from all his pains, fatigue and previous sins. The devotee wins pure virtue and becomes ever free.