A style of composition that makes pointed use of chromatic melodies and harmonies. A melodic passage is chromatic when it contains prominent motion by half-step; harmony is chromatic when the chord progression emphasizes voice-motion by half-step, or when the chords are routinely colored by half-step alteration of the ordinary diatonic pitches. The Romantic composers relied strongly and increasingly on chromaticism, for its ability to express intense emotion. (See also half step , semitone .) An excellent example of chromaticism is Wagner's Prelude to Tristan und Isolde. An instrument is considered chromatic when it can produce all the semitones: thus a valved trumpet is chromatic but a natural trumpet is not.