Ninja, not sure what link you want me to post? I've grown more DWC than any other hydro system, and it produces the most brilliantly white roots I've seen. No doubt some nutes colour your roots, but plenty of people use canna and I haven't heard anyone complain of it before.
Hydrogen peroxide also helps clean your roots, and freshens them up with the extra oxygen too I believe. I haven't used it myself, however I've seen people advise to use more pure (read: dangerous) h2o2 expressing fears of more fillers/things you don't want in the off the shelf pharmacy stuff. Hydro stores are apparently the place to look.
Although I dislike the bubbleponics fanboys, they are very devoted to DWC and Roseman has posted a lot of helpful information.. And the man loves his root porn, priding himself on their radiant whiteness and giving good info on how to get the same.
Is your air pump pumping fresh (cool preferably) air in large volumes? I believe that poor oxygen levels contributes to browning roots, based on the evidence that good aeration creates healthy fresh white roots.
I'm just spitballing here.