The specifics of your question are in the CGA Pamphlet C-6.2 of which I have not been able to find a viewable copy of online. When I inspect steel and aluminum cylinders (Propane) I look for defects, paint doesn't matter. There are currently no composite propane cylinders approved for use, so I don't get to inspect those. From what I have read in the CFR 49 Part 205.180(c) there is no restriction on painting a carbon fiber cylinder, only a coating that would impede the visual inspection. Propane cylinders have this same requirement (no rubber, tar or similar substances). Paint won't conceal a defect in a cylinder unless it is very thick.Â