Why is there a reddish hue on the surface of mother-of-pearl necklace ornaments?

The reddish tint visible on the surface is not contamination or a defect, but a trace unique to seashells.

MONDAY EDITION's mother-of-pearl necklace line uses ornaments carved from natural mother-of-pearl, and while the original reddish color of the seashell may remain on the surface, this is not a defect^[1][2]. In general, because natural mother-of-pearl is processed by carving the inner layer of a shell, the unique grain or thin red and dark pigments of the area from which each piece was harvested are revealed. Unlike artificial materials stamped out smoothly, slight variations in color and pattern from piece to piece are common characteristics of natural materials.

hmmm, the slightly different colors and grains shining through each piece are closer to unique proof that the ornament was carved from natural materials.