Bukhari

Hadith Commentary:
It is prohibited to observe mourning for more than three days over any deceased person, except for a husband, for whom a mourning period of four months and ten days is permitted.
Now, those people should reflect who, in the name of Husayn (radi Allahu anhu), observe mourning every year in Muharram, wear black clothes, and beat their chests in lamentation.
These people are certainly disobedient to Allah and His Messenger (sallallahu alayhi wa sallam).
May Allah guide them, ameen.
In this regard, Sunni individuals must also reflect that by acting contrary to the creed of Ahl al-Sunnah, they are committing a grave sin.
Hadahum Allah (may Allah guide them).

Hadith Commentary:
(1)
There is consensus among the scholars of the Ummah that a woman observing mourning (iddah) may not wear yellow or other colored garments, but she may wear black clothing, because black clothing is not for adornment but rather for the expression of grief and sorrow. Some scholars, in light of this hadith, have written that a woman may wear white clothing during these days, but if the white clothing is for adornment, then its use is prohibited. Similarly, when black clothing is for adornment, it should also not be used.

(2)
Imam Bukhari rahimahullah, through this chapter heading and the presented hadith, has established that there is no harm in using white and black striped garments. Likewise, cloth whose thread is colored before being woven may also be used, provided it is not for adornment.

And Allah knows best. (Fath al-Bari: 9/608)