i thing there is a bug of color folders sometimes maybe all time in the three folder dont dispaly the color :
I don't think it works for root drive-letters in the folder tree. (Do you really need to color those, though? There's only four of them... I'll add it to the to-do list anyway.)
It works fine for normal folders in the tree (so long as Preferences / Folder Tree / Appearance / Use configured file display colors for tree items is turned on).