Recently, an 8-year-old boy and his parents immigrated to Canada from Asia. Following their relocation, they organized his first health check-up at a local clinic. During the examination, the family physician noticed a bluish-grey pigmentation on the whites of the boy's eyes. Upon inquiry, the parents mentioned that the pigmentation had been present since the boy's birth. The boy was with no complaints of discomfort or pain in the eyes. The examination revealed a patchy, bluish-grey pigmentation in the medial aspect of the right eye, more intense near the limbus and fading peripherally and the sclera of his left eye, as shown in the image. There was no inflammation, swelling, or discharge from the eyes. No drooping of the eyelids. The boy's visual acuity was normal, and no abnormalities were detected on fundoscopic examination. Which of the following is the most likely diagnosis