in tlilli in tlapalli.

Headword: 
in tlilli in tlapalli.
Principal English Translation: 

the black, the red; the black ink, the red paint/dye; a metaphor for writings, especially early writings and paintings, such as codices (see attestations)

Attestations from sources in English: 

tlilli, tlapalli; or, in tlilli, in tlapalli; or in itlil, in itlapal = the black ink, the red paint, a metaphor for writing

mochi otechmocahuililitehuac in ipan sancto Euangelio. yhcuiliuhtoc tlapalotoc tlillotoc = before He departed he left for us all that lies written in the red and black [ink of ancient records] (central Mexico, early seventeenth century)
Codex Chimalpahin: Society and Politics in Mexico Tenochtitlan, Tlatelolco, Culhuacan, and Other Nahuatl Altepetl in Central Mexico; The Nahuatl and Spanish Annals and Accounts Collected and Recorded by don Domingo de San Antón Muñón Chimalpahin Quauhtlehuanitzin, eds. and transl. Arthur J. O. Anderson and Susan Schroeder (Norman: University of Oklahoma Press, 1997), vol. 2, 162–163.

Inamox, intlacuilol. Zan ic no yehoatl quitoznequi: intlil, intlapal. = Their books, their writings. This means the same as, their black and their red. (sixteenth century, central Mexico)
Thelma D. Sullivan, "Nahuatl Proverbs, Conundrums, and Metaphors, Collected by Sahagún," Estudios de Cultura Náhuatl 4 (1963), 176–177.

auh ayc polihuiz ayc ylcahuiz yn oquichihuaco yn intlillo yn intlapallo yn intenyo yn imitolloca yn imilnamicoca = And what they came to do, what they came to establish, their writings, their renown, their history, their memory will never perish, will never be forgotten in times to come. (central Mexico, early seventeenth century)
Codex Chimalpahin: Society and Politics in Mexico Tenochtitlan, Tlatelolco, Culhuacan, and Other Nahuatl Altepetl in Central Mexico; The Nahuatl and Spanish Annals and Accounts Collected and Recorded by don Domingo de San Antón Muñón Chimalpahin Quauhtlehuanitzin, eds. and transl. Arthur J. O. Anderson and Susan Schroeder (Norman: University of Oklahoma Press, 1997), vol. 1, 60–61.

Inamox, intlacuilol. Zan ic no yehoatl quitoznequi: intlil, intlapal. = Their books, their writings. This means the same as, their black and their red. (central Mexico, sixteenth-century)
Thelma D. Sullivan, "Nahuatl Proverbs, Conundrums, and Metaphors, Collected by Sahagún," Estudios de Cultura Náhuatl 4 (1963), 176–177.

Auh xicmocujtlavi in tlilli, in tlapalli, in amuxtli, in tlacujlolli: intloc innaoac ximocalaquj in iolizmatque, in tlamatinj = And take care [to understand] the writings, the books, the paintings. Enter with the prudent, the wise (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 6 -- Rhetoric and Moral Philosophy, No. 14, Part 7, eds. and transl. Arthur J. O. Anderson and Charles E. Dibble (Santa Fe and Salt Lake City: School of American Research and the University of Utah, 1961), 215.

We see this phrase used in the Codex Chimalpahin to refer to the ancient writings about Christ, so it was not exclusive to early American writings. (central Mexico, early seventeenth century)
Codex Chimalpahin: Society and Politics in Mexico Tenochtitlan, Tlatelolco, Culhuacan, and Other Nahuatl Altepetl in Central Mexico; The Nahuatl and Spanish Annals and Accounts Collected and Recorded by don Domingo de San Antón Muñón Chimalpahin Quauhtlehuanitzin
, eds. and transl. Arthur J. O. Anderson and Susan Schroeder (Norman: University of Oklahoma Press, 1997), vol. 2, 152–153.

Attestations from sources in Spanish: 

tictepotztocatihui yn itlil yn itlapal yn itlatecpantzin yn tlacatl tlahtohuani yn neçahualcoyotzin yn ye chicuehpohualxihuitl yhuan ỹ yemah tlacpohual xihuitl yhuan yn oc ye nepa ye huecauh xihuitl = Investigamos el negro y el colorado, y la ordenanza del señor tlatoani Nezahualcóyotl, hecha 170 años atrás, hace muchos años (Tetzcoco, 1585)
Benjamin Daniel Johnson, “Transcripción de los documentos Nahuas de Tezcoco en los Papeles de la Embajada Americana resguardados en el Archivo Histórico de la Biblioteca Nacional de Antropología e Historia de México”, en Documentos nahuas de Tezcoco, Vol. 1, ed. Javier Eduardo Ramírez López (Texcoco: Diócesis de Texcoco, 2018), 82–83.