Complex sentence: Itten's work on color is also said to be an inspiration for seasonal color analysis, Itten having been the first to associate color palettes with four types of people and designating those types with the names of seasons.
Split into simpler sentences: Itten's work on color is also said to be an inspiration for seasonal color analysis. Itten had been the first to associate color palettes with four types of people, and had designated those types with the names of seasons.