There's even a verb in Greek which means to 'dress in black', describing the old custom of widows wearing black for the rest of their lives after the death of their husbands.
One can still still many older women in Greek villages dressed entirely in black, following the old custom, though many modern women wear black for a much shorter time period (maybe a year). Death of a relative can also be the reason for wearing black for a period of time, and again, it is the women who dress entirely in black , the men simply wearing a black arm for a fairly short period of time.
I was told once of a not-so-young widow in an island village, whose husband had insisted that she dispense with this custom when he died, and she was seen at church after his death, wearing colors, setting the local village women to fierce gossiping. Indeed, these days many wear black in such places today only from fear of such censure from neighbors.
Customs such as these die hard in small villages, but there is far less observance of this custom among modern women, especially in cities, with younger women (especially those who have children in need of a father) often being encouraged to remarry.