all my roots are white,,when ever I have come across brown roots it generally means something is off,,to wet,,or to much nutrients ,, if the plants look okay not sure but the stunted one,,,may be the showing,of something being off a bit,,I have had clones or plants stunt most come out of it ,,,,if they get to much of certain things will almost lock the plant down in the sense that it will not let it take in enough water or nutrients ,during this stunted period,, but I agree Billy green thumb roots should be white and healthy looking