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White Doors are common types of Blast Shields that appear throughout the Metroid Prime Trilogy and are commonly opened by weapons of extreme cold. You may be looking for:
White Doors opened by the Ice Beam.
White Hatches opened by the Light Beam.
White Blast Shields opened by the Ice Missile.
Blast Shields in Wii versions of Metroid Prime 2: Echoes will turn white when locking (previously they turned grey)