Hadith: A woman should not mourn for any dead person more than three days except her husband for whom she should mourn four months and ten days. She should not wear dyed clothes (while in mourning) except ‘Asb (an unattractive Yemeni garment), nor should she apply kohl or touch perfume, except when she becomes purified (from her menses), as she may then apply a little Qust or Azhfār (types of incense)

عن أم عطية رضي الله عنها مرفوعاً: «لا تُحِدُّ امرأة على الميت فوق ثلاث، إلا على زوج: أربعة أشهر وعشرًا، ولا تلبس ثوبًا مَصْبُوغا إلا ثوب عَصْبٍ، ولا تكتحل، ولا تَمَسُّ طيبًا إلا إذا طهرت: نبُذة من قُسط أو أظْفَار».
[صحيح] - [متفق عليه]

Umm ‘Atiyyah (may Allah be pleased with her) reported that the Prophet (may Allah's peace and blessings be upon him) said: "A woman should not mourn for any dead person more than three days except her husband for whom she should mourn four months and ten days. She should not wear dyed clothes (while in mourning) except ‘Asb (an unattractive Yemeni garment), nor should she apply kohl or touch perfume, except when she becomes purified (after her menses), as she may then apply a little Qust or Azhfār (types of incense)."
Sahih/Authentic. - [Al-Bukhari and Muslim]

Explanation

In this Hadīth, the Prophet (may Allah's peace and blessings be upon him) forbade women from mourning the dead for more than three days, which are sufficient to fulfill the rights of kin as well as provide solace to the grief-stricken. This is as long as the dead person is not the woman’s husband, for in this case the mourning period must be four months and ten days, in order to fulfill his enormous right as well as to ensure safeguarding herself during the ‘Iddah. Mourning includes abandoning any type of adornment, such as perfume, kohl, jewelry, and beautiful garments. Hence, she does not use any of these things. This only applies to the woman whose husband died. If the deceased is other than the husband, she may mourn for three days only if she wishes. Regarding the clothes that are dyed for reasons other than adornment, there is no harm in wearing them no matter what color they are. Likewise, she may use a small amount of a substance that removes unpleasant odors on her private parts after she becomes purified from her menstrual period, and the intent is not to perfume this spot, which is not a spot for adornment.