The application randomly picks default symbology colors each time you add new data to your map. You can manually change the symbology through later properties but I don't think you can control what the app picks as a default. Transparency is something you need to manually set within layer properties. ArcMap won't automatically set transparency settings.
Python arcpy.mapping could also be used. Author a layer file (.lyr) and use the UpdateLayer function to apply the symbology in the layer file to the layer of interest.
