Piet Mondrian began his career painting realistic scenes, but over time his style became more abstract and simplified. He eliminated details and only used the primary colors of red, yellow, and blue along with black, white, and gray. Mondrian was always experimenting with line thickness and placement to achieve balance in his compositions. In his later years, the straight lines of New York City may have influenced his abstract geometric paintings consisting of only rectangles of pure color separated by thick black lines.