That looks like serious bad root rot to me, I got pics of my root rot and mine are still brownish!
I think I have root rot, my roots have stopped growing, they float in the water, and they have a brownish color to them. They arnt slimey or black anywhere, but maybe i caught it before then. At first I just added hygrozine to the nutrient solution of my DWC and within 2 days the water turned to a murky brownish color and my ph skyrocketed from 5.8 to 6.5. I then changed the res to have only pure tap water and hygrozine. I hope this will kill my root rot.
Thats what Im doing, dont know if it will work, some people say you gotta cut the roots off. I did this a few days ago to my second res that had even worst root rot, I took a 1ft plants roots completely off, just leaving about an inch of roots from the main stem. She's hanging in there thank god, dont know about the others though.