You know, they may not have even realized it was an exact copy until they got it home. There could have been a limited choice of colors, or they could have subconsciously picked that color without realizing why they liked it.
Of course, if they have young kids, you could give them a copy of Robert Munsch's book "Stephanie's Ponytail."
(short synopsis: Stephanie wears a ponytail on the top of her head to school. Whole class calls it ugly, but wears the exact same thing the next day. Repeat with various ponytail styles until Stephanie announces one day she plans to come with a shaved head the next day. The next day the whole school sports a shaved head...except Stephanie.)