to become, end up, or turn out black (see Molina)
caputzaui. (pret. ocaputzauh.) pararse negro. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 12v. col. 1. Thanks to Joe Campbell for providing the transcription.
M has caputzaui with the same sense.