Android :: First App Changing Background Color From List Of Specified Colors

This is my first app so finding my way around bit by bit and have been experimenting a little and would like to change the background colour to a colour from a list.Currently it loads a white background specified in strings.xml <color name="all_white">#FFFFFF</color> This is used in main.xml:android: background=" @color/all _white"Ideally I would like to change the colour in OnCreate() to a colour of my choice. I have tried setBackground Drawable but it doesnt seem to work?This is my code:public class TestActivity extends Activity double dimValPercent = 100; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super. onCreate (savedInstance State); setContentView(R.layout.main); SetDimLevel(dimValPercent);SetBackground(); return;}public void SetBackground(){getWindow().setBackgroundDrawable( new ColorDrawable (color.all_blue) );