Use a color wheel to find the best color palette according to your sectional sofa or existing interior. If you are not familiar with the color wheel, find your main color and the color over it. Then the two colors on each of their left and right sides can include your palette when choosing pillows, but a maximum of five colors will suffice.
You can also use several neutral shades for the majority of your sofa cushions and then pop in some bold colors. For example, have a neutral-colored pillow paired with a printed pillow on each section corner. Then add a color to the angle to increase the interest in the symmetrical look.