The term 'Spectrum Part' refers to three components of the visible light spectrum: HUE, INDIGO, and COLOR. HUE is a three-letter word that describes the gradation of colors in the spectrum, from red to violet. INDIGO is a six-letter word that is a deep blue-violet COLOR, located between blue and violet in the visible light spectrum. COLOR is a five-letter word that is used to describe the range of visible light that can be perceived by the human eye.