Android Alternate row Colors in ListView

public class ListView extends  ListActivity {

static String item;

public void onCreate(Bundle icicle) {
            super.onCreate(icicle);

            ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, Str.S);
            setListAdapter(adapter);

      }

This is my list view class which works nice and it takes the strings from a class called Str and display them in a listview, the problem is the listview style isn't nice, it's black with the strings in white.

I want them to be alternative each row has a color.

I tried many tutorials but none was clear enough .. How do I make Alternative Color for each row .. ex. row1 Blue, row 2 White, row 3 Blue, row 4 White, etc..