^^^She had purple hair in the PC-98 era. This was less a stylistic choice than a result of the technical limitations on the games' colour palettes. When the games moved to Windows, and to 16-million-colour palettes, she started being depicted with black hair. You'll also note that Marisa was usually depicted with purple clothes on the PC-98 also. (On the other hand, Marisa was depicted with red hair in SoEW. That was definitely a design change.)