===A singular exception doesn't really change the probability of Hume's thesis===
Hume states that the model of rationality that humans ''use'' and ''must use'' with regard to reasonings about matters of fact is not [[classical logic]], but rather some kind of [[probabilistic logic]] where we associate a [[relative probability]] to factual statements (in fact, recalling [[John Locke|Locke]], Hume calls reasoning about matters of fact as merely ''probable'', and contrasts it with the ''demonstrative'' reasoning about relations of ideas).<ref name="Section 6">Hume writes in ''Section VI'' (On Probability) of the ''[[An Enquiry Concerning Human Understanding|Enquiry]]'': «Mr. Locke divides all arguments into ''demonstrative'' and ''probable''. In this view, we must say, that it is only probable that all men must die, or that the sun will rise tomorrow. But to conform our language more to common use, we ought to divide arguments into ''demonstrations, proofs,'' and ''probabilities''. By proofs meaning such arguments from experience as leave no room for doubt or opposition».</ref> This is especially clear in [[Of Miracles|Hume's treatment of miracles]] in ''Section X'' of the ''[[An Enquiry Concerning Human Understanding|Enquiry]]'', in which he claims that the relative probability of a certain factual thesis (in this case the thesis that "miracles do occur") ''is'' and ''must'' be evaluated by weighting all the evidences in favour of it with all the contrary evidences.
Since Hume's thesis that "all simple ideas come from simple impressions" is a matter of fact (ie. a factual statement), we can associate a probability to it. And the only way of evaluating the probability of this thesis is by weighting all the evidences. Since, except the "missing shade of blue", ''all'' the countless other direct evidences favour it, the influence (via [[Bayes theorem]]) of this singular contrary evidence on the probability of Hume's thesis can reasonably be expected to be minimal. And that's why Hume can reasonably say that this contrary evidence can be disregarded
