What is the artist communicating in Non-Representational paintings?

If subject matter is what is being depicted in a work of art, what is the subject of non-representational works such as Blue, Orange, Red by Mark Rothko and Autumn Rhythm by Jackson Pollock? What is Donald Judd communicating in his piece titled 100 untitled works in mill aluminum? What do you think the content is? How does the form help the artist express the content? Identify visual elements and principles of design in your analysis.