Is this some rule that is well established and unchangable? Ofcourse not. It was evolved based on convenience. My reading also tells me that courts had judges from four madhabs.
I haven't read it but if there is some unambiguous proof that is not possible to be counter argued, then you can point it out here. My point simply was based on the context of time where shariah state should start by applying what is most evident and well established and agreed; rather than applying ijthihad of every mufti here and there. The state should function in a manner that is consistent and built on strong principles and not act upon speculative ijthihad of every new mufti. Just because some past scholar allowed a certain dress color code for dhimmis don't mean a certain mufti can say "hey this scholar allowed it, so are you smarter than him? " and then apply dress color code to identify dhmmis. That is equivalent to salafis who fetch for opinions without any principles.