Naum Gabo created these paintings to illustrate from his 1959 lectures on color, Of Divers Arts. Though they are beautiful on their own, I think they become even more beautiful when you understand what they represent.
From the Gabo lecture:
“All colors, even in their seemingly identical hues, have a different identity in our vision of them. One and the same color acts differently on different surfaces. Colors change with the change of their place in space or on a surface, and their identity also varies with the time at which they appear in the field of our vision. They change not only according to the neighboring color—a fact by now known to every schoolboy—but in relation to the frame of our vision and its axis, i.e., to right or left of the axis, and up or down from it”
To further illustrate his point, these paintings are mounted on a motorized mechanism that spins each painting like this.