This determinative was originally two separate signs, one with a seated man putting his hand to his mouth as a determinative for eating, and one where the seated man’s hand did not touch the mouth but was depicted palm-outward as a determinative for speech, intellect, and exclamations. Later the latter sign was subsumed by the former. This and other glyphs depicting men conventionally color the skin red; the hair is typically black, and the clothing white (sometimes with black outlines or details).
During the Heracleopolitan Period, confusion of this sign with the seated man
Gardiner, Alan (1957) Egyptian Grammar: Being an Introduction to the Study of Hieroglyphs, third edition, Oxford: Griffith Institute, →ISBN, page 442
Betrò, Maria Carmela (1995) Geroglifici: 580 Segni per Capire l'Antico Egitto, Milan: Arnoldo Mondadori Editore S.p.A., →ISBN
Henry George Fischer (1988) Ancient Egyptian Calligraphy: A Beginner’s Guide to Writing Hieroglyphs, New York: Metropolitan Museum of Art, →ISBN, page 15