Chromatic harmony means harmony (chords) which use notes which do not belong to the key the music is in (they are not in the key signature). Although Bach in the 18th century used chromatic harmony it was the 19th-century composers who used it more and more.
Whatever the emotion, Romantic composers sought to describe feelings and the deeper truths of life. In doing so, the emotional expression of the work was elevated and celebrated. The emphasis on feeling often led to fuller, richer melodies and harmonies, resulting in sounds that reflected greater emotion.
