Abstract: A substrate containing magnesium treated with color development, according to the present invention, comprises a coating having a structure in which crystals having a plate-shaped structure are horizontally even and densely stacked on a matrix containing magnesium, thereby maintaining a texture and sheen unique to the metal while enabling even development of a plurality of colors on the surface by controlling the average thickness of the coating, according to the amount of stacking of the crystals, and thus can be useful in areas using metal materials, such as external materials for construction, vehicle interiors, and especially in electrical and electronic parts material fields such as in mobile phone case parts.