The authors agree that this surname derives from a compound formed by two personal names: Nicola, in its reduced form Cola, and Giovanni, in its reduced dialectal variants Ianni or Janni. The bearers would have taken the surname from an ancestor who bore that combination of names.

V. Blunda proposes a different etymology: according to him, the surname comes from the Greek Calojànnes, "John the good", composed of the prefix kalo- ("good") and the personal name Iànnes, a hypocoristic of Giovanni. Blunda frames it within a series of surnames formed with that same prefix, such as Colamasi, Colàngelo and Colantoni.

F. Miranda identifies the main variants of the surname: Colagiovanni, Colajanni, Colanni and Colianni. He notes that the surname is of Apulian origin and that in Sicily it is present in almost all the provinces, with concentration especially in the Palermo, Catania, Syracuse, Caltanissetta and Enna areas, in addition to the Messina area. He also records ramifications in Lombardy, Abruzzo, Piedmont, the Marche, Campania and Basilicata, with clusters in Puglia and in the province of Rome.

E. Rossoni specifies the geographical distribution of each variant: Colaianni presents specific areas in Sicily, between Enna and Catania, in the Bari area, in the L'Aquila area and in the province of Rome; Colajanni is typically Sicilian, of the Palermo, Caltanissetta, Enna and Catania areas; Colanni is practically unique; and Colianni appears as peculiar to Calascibetta, in the Enna area.