First, note that this border is drawn to help a user know the zone where he can click to select a piece of furniture. It's not drawn in printed and exported images (SVG and clipboard image).
You can change its color only by program at this time. Either change getFurnitureOutlineColor method in PlanComponent class, or override this method in a subclass of PlanComponent that you will instantiate in a customized ViewFactory. If you want to remove it completely, return a fully transparent color.