brownish isn't that bad as long as they're firm and no other signs above 'ground', nutes do play a part in discolouration. mostly you find the issue on the upper part of the plant which leads to a root check and problem id, but the question asked at the begining leads me to believe that the plant simply reacted according to its environment and created a hairy root mass to absorbe moisture in the surround air from the nuts in the bottom of the growing chamber, but for this to be the case they should be whitish since they've had little direct contact with the nutes. this is my understanding of the query. as i reread the roots are white so there is no negative for the root mass, quite good actually. i wouldn't worry about it wdldtoker