Ruling on woman wearing black during her monthly period
Question

                I heard that it is not permissible for a woman to wear black during her period, because the Ka‘bah is black, and this signals a lack of respect for it. Is this true? Even my husband said to me recently that it is also not permissible to wear black underwear, out of respect for the colour of the Ka‘bah. What is your opinion on this?.
Praise be to Allah.
      There is nothing wrong with a woman wearing black during 
      her monthly period. This is for two reasons: 

    1.

    The basic principle is that things are permissible and there 
    is nothing in sharee‘ah to say that a woman cannot wear any particular 
    colour during her period, whether that is black or any other colour. So it 
    is essential to adhere to the basic principle. 

    2.

    The fact that the Ka‘bah is covered with black is not a 
    matter that enjoined, because there is nothing in the Sunnah to that effect. 
    Rather it is the custom of people at present. If the Holy Ka‘bah were to be 
    covered in some other appropriate colour, there would be nothing wrong with 
    that. Black is not a special colour for the Holy Ka‘bah such that it would 
    form the basis for a ruling that it is not permissible for a menstruating 
    woman to wear black. 

    Rather, if we were to assume that the colour of the covering 
    of the Ka‘bah is something enjoined, that would not in itself indicate that 
    it is forbidden for a menstruating woman to wear black or that it is 
    disliked for her to do so. 

    One should beware of things that are said or spread in 
    rumours stating that something is haraam or halaal, when there is no basis 
    for it in sharee‘ah. Allah, may He be exalted, says (interpretation of the 
    meaning):

    “Say (O Muhammadto these 
    polytheists): ‘Tell me, what provision Allaah has sent down to you! And you 
    have made of it lawful and unlawful.’ Say (O Muhammad): ‘Has Allaah 
    permitted you (to do so), or do you invent a lie against Allaah?’

    60. And what think those who invent a lie against Allaah, 
    on the Day of Resurrection? [i.e. Do they think that they will be forgiven 
    and excused! Nay, they will have an eternal punishment in the fire of Hell.] 
    Truly, Allaah is full of bounty to mankind, but most of them are ungrateful”

    [Yoonus 10:59-60]. 

    Al-Haafiz Ibn Katheer (may Allah have mercy on him) said: 

    Allah denounces the one who forbids what Allah has permitted, 
    or permits what Allah has forbidden on the basis of mere opinions or whims 
    and desires, for which there is no evidence. Then He warns them against that 
    on the Day of Resurrection and says (interpretation of the meaning): “And 
    what think those who invent a lie against Allaah, on the Day of 
    Resurrection?” i.e., what do they think will happen to them on the Day 
    they return to Us, the Day of Resurrection?! 

    End quote. Tafseer Ibn Katheer, 4/276 

    And Allah knows best.