´It was narrated from Safiyyah bint Shaibah, from Umm Salamah, the wife of the Prophet, that the Prophet said:` "The woman whose husband has died should not wear clothes that are dyed with safflower or red clay, and she should not use dye nor kohl."
Hadith Referenceسنن نسائي / كتاب الطلاق / 3565
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:إسناده حسن
It is prohibited to wear cloth that has been dyed afterwards, regardless of what substance or color it has been dyed with. "Mishq" refers to red clay (geru) with which the cloth used to be dyed. Nowadays, almost every cloth is dyed only after being woven, so it is difficult to find such cloth whose thread was dyed before weaving. Therefore, in the present time, such plain clothes should be worn in which, generally, there is no display of adornment, which are not flashy, floral, or of bright colors—for example: old clothes, etc. The objective is to abandon adornment. And Allah knows best.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 3565
Narrated Umm Salamah, Ummul Muminin: The Prophet ﷺ said: A woman whose husband has died must not wear clothes dyed with safflower (usfur) or with red ochre (mishq) and ornaments. She must not apply henna and collyrium.
Shaykh Umar Farooq Saeedi
Benefits and Issues: These matters are part of adornment; therefore, it is obligatory to refrain from them during the days of ‘iddah (waiting period).
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 2304