As I discussed here, the duty of an insurer to defend an insured is determined by the "eight corners test." Under that test, "if the allegations of the complaint are 'reasonably susceptible' of an interpretation that they state or adumbrate a claim covered by the policy terms, the insurer has a duty to defend." (The "eight corners" comes from comparing the four corners of the complaint to the four corners of the insurance policy.)
But what about when the allegations of the underlying complaint are silent as to an issue that is important for determining coverage? For example, what if the insurance policy provides coverage for all blue cars owned by Lucy Smith? Smith is sued following a motor vehicle accident. The underlying complaint will probably allege the make and model of the car Smith was driving, but it is unlikely to state the color of the car because the color is irrelevant to Smith's liability. Can the insurer refuse to defend because its investigation reveals that the car Smith was driving at the time of the accident was yellow, and so not covered by the "blue car policy"?
Yes. In Farm Family Mut. Ins. Co. v. Whelpley, 54 Mass. App. Ct. 743, 747 (2002), the court held that there is an exception to the eight corners test for "the existence of an undisputed extrinsic fact that takes the case outside the coverage and that will not be litigated at trial of the underlying action."