Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
There is no particular colour that is observed in the Hijab of a woman but there are many other conditions that should be fulfilled. One of those conditions is that the Hijab must not be worn as a display so that it motivates seduction.
It should cover the woman’s whole body. For more details in this subject, please read the Fatwa: 83702.
Allah knows best.