On a much smaller scale, and admittedly with a smooth surface, I was surprised to see how the colour bands were applied to vintage Erie resistors. The paint was simply sprayed through a slot onto the rotating tubes (before the resistor itself was inserted). You can see it from about 01:40 onwards here
https://www.iwm.org.uk/collections/i...ect/1060039091. The results were generally much more sharp-edged and well-aligned than I'd have expected, despite the slots being quite a long way from the tubes and the tubes themselves not being located very exactly in their holders.
Cheers,
GJ