K-line running on DC controller, K-line freight car boxes different colors

Hello everyone, 

Got a couple of questions.  I have a Bachmann Spectrum magnum ultra plus DC controller.  I read in this forum you could run K-line and Lionel O27 scale with DC, so I set up a loop of train and ran two K- line loco with the above controller.  The controller has brake, momentum that worked on the K-line loco's.  I was able to run two at the same time.  Am I going to damage the loco's?   My other question is on the different color K-line freight car boxes.  I have saw black, black and gold, black and yellow, Maroon  and gold, blue and gold, etc. are colors of boxes indicators of different quality?😁

thanks for reading