All of your pens posted tonight look great.
What is reverse painted?
Drill the blank, paint the inside of the drilled hole, (with a q tip or the likes) allow to dry and then glue the tubes in place.
That is done rather than just painting the outside of the tubes.
I tend to use epoxy glue with a little colour acrylic pain mixed in it to match the blanks, helps keep it a better colour on my view and less risk of the tube showing through.