I'd vote no carpet on the inside of the tubes... carpet will just hang-up tips/guides/hooks, and get frayed. Even a slight flare on the PVC will help slide the rods into the tubes, and keep tubes from pushing forward.
My guess is any paint (even plastic paint) will likely get beat up with constant rod in/out. I'd leave them white.

Another idea to finish off the tubes, would be to slice off thin sections of a PVC coupling (like 1/8 - 1/4" thick rings) and PVC cement them on the end of the pipe. Sand the face once the cement cures and would make a nice flanged stop.