Does a woman should cover hear head with one cover or two covers?

Question

According to shariah, is that ok if a woman covers her head with one cover or she needs to cover with two covers or more?

Answer 1

If one cover conceals her hair completely, and does not reveal the colour of it due to thinness, then this is sufficient.

Answer 2

Allah ordered humans to cover, as for the how HE left them a certain liberty.
Allah said addressing both men and women:

• O children of Adam, We have bestowed upon you clothing to conceal your private parts and as adornment. But the clothing of righteousness - that is best. That is from the signs of Allah that perhaps they will remember.
  (7:26)

And explicitly for women (after addressing men too in 24:30):

• And tell the believing women to reduce [some] of their vision and guard their private parts and not expose their adornment except that which [necessarily] appears thereof and to wrap [a portion of] their headcovers over their chests and not expose their adornment except to their husbands, their fathers, their husbands' fathers, their sons, their husbands' sons, their brothers, their brothers' sons, their sisters' sons, their women, that which their right hands possess, or those male attendants having no physical desire, or children who are not yet aware of the private aspects of women. And let them not stamp their feet to make known what they conceal of their adornment. And turn to Allah in repentance, all of you, O believers, that you might succeed. (24:31)

And HE further ordered:

• O Prophet, tell your wives and your daughters and the women of the believers to bring down over themselves [part] of their outer garments. That is more suitable that they will be known and not be abused. And ever is Allah Forgiving and Merciful. (33:59)

All these verses tell us that we should cover ourselves and our private parts and what is regarded as 'awrah. As for the how this might be explained a bit more in the sunnah, but still there's no limitation or fixed amount set for the covering tools or garments.