The correct answer is B) white. When a submarine surfaces from periscope depth, it is required to send up white signal flares to alert other vessels in the area of its presence and position. This is a standard safety protocol for submarine operations, as the white flares are highly visible and distinguish the submarine's surfacing from other types of maritime distress signals, which typically use red or orange flares. The other answer choices are incorrect because red, green, and yellow flares are not the standard signaling method for a submarine surfacing. These color flares are typically used for different purposes, such as distress signals or navigational markers, but do not specifically indicate a submarine surfacing.