Color therapy--or chromotherapy--work with the concept that the visible spectrum of ROYGBIV affects the human energy field (aura) in a positive way. You've heard the idioms "green with envy", "out of the blue", "paint the town red", "look at the world through rose colored glasses", etc.. They denote how color makes us feel. We're responding to its frequency and vibration and that's why some colors are pleasing and others are not. There is a definite element of subjectivity involved in the psychology of color as well, including culture, generational perspectives, and personal preferences.