1. Error coins of NCLT are generally scarcer than error coins on regular coinage since they are more carefully inspected, though, as with anything, human error can always result in an error getting out.
2. Yes, but see also #4 below.
3. No answer, since even the examples you gave all vary considerably.
4. Coloured coins are relatively new, and almost all are NCLT issues, so errors on them would be few, only because the number of coloured coins relative to non-colored coins is low.
That being said, the main issue with a colored coin missing one or more parts of the color is that it would be somewhat difficult to prove that it came without colouring (rather than being removed) and so would likely only be accepted (at least in North America) if a certification company guaranteed it.