I was repotting my phals from the store's pure sphag medium into s/h to see how things went. My roots looked pretty sorry though. I mean, there weren't a lot of dead ones, but some were a really pale yellow. Here are some pictures:
Green, white, pale yellow (even brown) are good ..
Mushy and black are rotten ...
You can test them by gently applying a little pressure to the root .. if it's firm, it's good ..
if it's mushy .. then it's from the tushy ... and time to flush it ..
If the outer white covering is cracked, the root is still good and can still absorb water and nutrients .. don't cut them off .. (again, unless they are mushy)