The progression of a painter's work, as it travels in time from point to point, will be toward clarity: toward the elimination of all obstacles between the painter and the idea, and between the idea and the observer.
By 1950 Rothko had arrived at his signature style, achieving his ideal of "the simple expression of the complex thought." This most often took the form of compositions of two to four rectangular forms, aligned vertically against a color ground, for example Untitled, 1955. Within this format, Rothko used a broad spectrum of colors and tones, and a variety of formal relationships, to create moods and atmospheric effects ranging from dramatic to sober, to lyric. Rothko's work darkened significantly during the 1950s, as seen in Untitled, 1957. By 1958 he often abandoned radiant colors in favor a darker palette of red, maroon, brown, and black, especially in a series of public mural projects that preoccupied much of his time in the last decade of his life.
Following an aneurism in 1968, Rothko relinquished his work on large canvases and concentrated on works on paper. Many of these were mounted on panel or fabric, giving them the appearance of unframed canvases. Untitled, 1969, is from a group of brown or black and gray paintings produced during the end of his life. In them, Rothko further condensed his composition to a fundamental contrast of colors, tones, and surfaces. Dark colors did not solely dominate his palette at this time, however, as seen in the vivid red painting, Untitled, dated to 1970 (no. 21).