Is the wife who did not inform her husband of her contracting and recovering from vitiligo before marriage sinful, and must she inform him now?

There is no sin upon you for not informing your husband of the matter, as long as you have recovered from it. Even if you had not recovered, vitiligo is not among the defects that affect marriage. Al-Mawardi said: "As for vitiligo, it is a change in skin color that does not diminish one's blood and it fades, and souls are not repelled by it, so there is no option [for annulment] due to it." Conceal yourself and be keen on maintaining a good marital relationship.