The localized bluish-gray discoloration near a tooth that underwent apical surgery is most consistent with an amalgam tattoo. This occurs when metallic particles from dental materials (such as amalgam used during surgery) become embedded in the gingival tissues, causing a persistent pigmentation. The lesion is typically asymptomatic, well-defined, and does not change over time. Other options are less likely given the history and appearance; for example, hemangiomas are usually red or purple and raised, melanotic macules are generally smaller and unrelated to surgery, and Kaposi sarcoma is uncommon and usually seen in immunocompromised patients.

Reference: Oral Pathology for the Dental Hygienist, 7th Edition.