What a wonderful fish, I asked Sven Kullander for any hint about the identification and he was kind enough to give me the following information:
Sorry not to be of much help with this one:
(1) yes, the photos show a C. facetum group species.
(2) it is probably from north of the area where we worked, and there are many forms/species in the São Paulo area and slightly northward which have not been documented. A Brazilian student presented a Masters thesis of them many years ago, but I do not possess a copy, and I forgot the name of the student. Seems to have only 6 anal spines which is compatible with such a range.
(3) I am familiar with the Uruguay and Paraná basin forms, and none of them to my knowledge has this breeding color.
(4) a PhD candidate of mine did produce a licentiate thesis (= halfway PhD) which was a revision of that southern part of the facetum group. He suddenly left the university and museum just before obtaining the degree nearly a year ago, and we have no idea where he is or is up to now. He is said to have collected or had plans to collect in Mexico late last year.
So, we have another mystery to resolve! Thanks so much for posting your wonderful pictures!