Together with his brother Gianni, Colombo developed the idea of prismatic lamps like the lamp Acrilica(1962). His first design for Kartell was the chair No.4801 (1963–1967) which consisted of three assembled plywood elements. The flowing elements of his chair were a foretaste of his later plastic designs, like the chair universale No.4860 (1965–1967), which was the first seating for adults made of ABS.

In 1964 Colombo received the IN-Arch prize for his room conception of a hotel in Sardinia (1962–1964). In 1967 and 1968, he was awarded ADI (Associazione per il Designo Industriale) prize. In 1970 he received the Compasso d'Oro award.