Jane,
Your question is understood, and it is a good one. . But it seems to me there is no definitive answer because the effect depends on which kit you use. . The effect also depends on the basic color of your blank, as well as on its manufactured structure which creates the "scale" patterning.
The effect will depend on the degree of transparency of the turned blank, and that, of course, depends on the wall thickness of the turned blank, which, in turn, depends on the kit.
It also depends on your style of turning, whether you turn your blanks straight-sided or slightly bulged, or whatever.
If you are putting the blank on a PSI Executive kit, and if you are turning straight-sided (no bulge), then the wall thickness is uniformly about 0.032", one of the thinnest in the world's arsenal of pen kits. . On the other hand, if you are turning a PSI Music kit, and doing it straight-sided, then the wall thickness is about 0.142" at the thickest part. . So the effect of painting the tube will be quite different between these two examples.
I am interested in Ed's response so I will stay tuned to read what he has to say. . Be sure to post any results or ideas you come up with also, please.