Is the abaya part of the hijab, and what is the opinion of the four imams concerning it, and why the black color, and when did it appear?

We have previously mentioned in fatwas 40179 and 34766 that the hijab is achieved by an abaya or other garments, and by the color black or other colors, provided that it is concealing, opaque, not transparent, loose-fitting so as not to define the 'awrah, and not a garment of fame or specific to men.