when l tried to edit a model(done by other architects), i went to the Project Browser, under the Family i find baluster. But not sure whether coz railing is a system family or some other reasons (hope some one could help to explain), l couldn't directly edit type or edit bluster family . What l did was to choose the baluster family and create a component in anywhere of the project, and then l click the baluster l created and only after this i can double click the component and go to family edit section. I changed the material and color inside the family edit section and load into project, the problem finally solved.