Ben,
What you are seeing is a glue visibility issue. You are actually seeing the bond line between the blank and the tube
Try painting the inside of the blank instead.
Krylon fusion works great.
In fact, drill a size small, then sand up to size starting with 180 then 220 grit on the inside of the blank, and I think you will be happier with the results. Do not go too fine, as the paint needs some tooth to bite into.
If you are getting interior chipoout on the blank due to drilling issues, then you will see those defects as well.
A sharp drill, and a good pecking technique, along with the sand and paint of the inside of the blank will yield a great finished product