All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
There is no doubt that a particular color is not required in the hijaab of a Muslim woman, but it should not be of a color that makes it an adornment in itself and attracts the attention of men towards looking at her, as perhaps she causes temptation to their hearts because of it.
The Permanent Committee of Iftaa’ was asked, “Is it permissible for a woman to go out wearing an adorned dress?”
The Committee replied, “It is not permissible for a woman to go out wearing an adorned dress that attracts attention because that incites men and causes them to be tempted in their religion, and this dress may expose her to harassment.”
Hence, if this condition is met, (i.e. it is not an adornment in itself); then it does not harm if it is praised by some people for other considerations, and a woman is not obliged to wear black or dull colors.
If the family gathering which you mentioned includes the presence of non-Maham (marriageable) men, then she must abide by the hijaab with its conditions, but if she is in the presence of women like her, then the matter is flexible. Please note that you should be cautious of mixing and the like in family gatherings where non-Mahram men are present.
Allah knows best.