The Dummy Object is one of many Helper Objects:

The dummy object is implemented as a NURBS curve list. To modify its settings, the custom parameter set nested beneath the NURBS curve list object must be selected.

• Icon Size - The size of the icon, in world units.
• Use Custom Icon - Allows a custom icon to be associated with the dummy. Once this icon is selected, the file is no longer needed.
• Use Default Icon - Resets the icon to be the default.
• Text - General text. Unlike other versions of the OgreMax Scene Exporter, this text is not displayed in the viewports.

Other Settings

The dummy object color can be modified with the object's Wireframe Color setting: