Apply a paint color to base plate that matches the floor or wall around the structural steel. This color will blend the base plate into the background. Any paint store can match the exact color you need if you bring in a sample of the material.
Build wood boxes to cover the base plates and supporting columns. Paint them to a desirable color to work with the room's colors.
Have an artist paint the base plates in interesting ways to draw attention to them. Certain types of modern design work well with cold steel structures.
Lay matching flooring over the base plates to hide them from view.