Some philosophers seem to think that vagueness should be included: borderline cases provide further cases of apparent faultless disagreement. But this, however, does not seem to be so. Take Jason and his husband Justin, and consider a borderline green towel. Typically, I submit, they would not respond to it by taking a view as to whether the towel is green or not. They would simply lack the judgements that they would naturally express in an ordinary context by asserting ‘The towel is green’ or ‘The towel is nor green’ with its literal meaning: rather, if questioned about it, they would easily converge in something like that ‘it sort of is and sort of isn’t,’ ‘it's greenish,’ etc.—and they would be rational in so doing. But then they would lack the building blocks for the appearance of faultless disagreement clearly present in the other case considered above: the (contrasting) judgements. Hannah and Sarah do typically form polar opinions with respect to issues such as whether Homer Simpson is funny; Jason and Justin typically do not form such verdicts with respect to issues such as whether the towel is green.
So this is in essence why I think that vagueness does not provide further cases of apparent faultless disagreement: with respect to borderline cases, people typically do not respond by taking a view—unlike what is the case in genuine cases of apparent faultless disagreement. I have written a paper trying to provide further considerations in favor of this claim. Comments and objections very welcome!