Paul Klee's explorations of the power of color

'Color possesses me," Paul Klee said – a sudden, revelatory exclamation – early in his career. It was the point when he realized he was truly "an artist." He continued to explore and analyze the expressive possibilities of line and form, structure and rhythm in the (often deceptively whimsical) intimacy of his contemplative paintings. But it was color and its power that remained the most unfathomable factor in his mysterious vision.

The painting shown here is unusual in several ways. Its title, for a start, is not typical – "Late Evening Looking Out of the Woods." Most of Klee's titles are much less descriptive of a specific personal experience. Evidently his intention was a direct record of something witnessed in a particular place at an exact time.

This painting is also unusual in its clearly rushed execution and apparently almost spontaneous improvisation. It shares its boldness with the stronger, less meticulous and intricate paintings that belong to his final years. But this blue and brown painting can hardly be called a typical Klee. Many Klees are instantly recognizable as his. This is not.

Its accumulation of blue biomorphic forms is certainly responsive to his underlying sense of abstract structure. But the painting is, I believe, essentially representing an optical phenomenon – the way in which the sky at twilight becomes an intense, oddly bright blue and, if glimpsed through trees and leaves, fiercely pushes through their interstices so that they are virtually background silhouettes. He also has captured that reduction of colors to a close tonality that is seen in the twilight.It is as if color is perceived with the eyes shut.

The forest seems to have had profound significance for Klee. Two years later he painted "In the Depths of the Forest" in which the color is even further reduced – to a rich, warm, deep shade of green. This is a masterpiece, a dream painting in which botanically weird plant forms loom as only Klee could conceive them.

The "Late Evening" painting (it belongs to the St. Louis Art Museum and is one of 10 Klees of different periods selected for a small exhibition-tribute by Eric Lutz) is less profoundly visionary. But it does add an unexpected note to one's overall sense of this extraordinary artist's experimental originality.

• 'Paul Klee' is at the St. Louis Art Museum until July 9.