It is possible to decorate a Styrofoam column by painting the column with spray or acrylic paint, draping it with patterned or solid colored fabric, or wrapping it with greenery. Additionally, you can top it with flowers, topiaries or Tchotchkes.
If you want to make the column look more realistic, the best option is paint it. Spray paints and acrylic paints work best on Styrofoam. This option also allows you to choose the color that looks best for your design.
Another option is to choose a fabric in a color and pattern that fits your needs and wrap it around the column. Wrap it around once and tie it off with a bow, or continue wrapping it around until the fabric is wrapped around the entire length of the column.
Finally, you can put something on the top of the column, such as small vases with plants, foam statues, or any other decoration that fits your needs.