Passing views between Activities

i've got a "simple" question: How do i pass a view from an Activity to another?

In my case:

I've got a MainActivity with setContentView(R.layout.activity_main); In this activity_main i've declared a Relativelayout, whose Backgroundcolor I wanna change from another Activity, that gets its setContentView from an .xml file, where you cant find this RelativeLayout. How do i do that?

Thanks for the quick answer!

MainActivity.java

public class MainActivity extends AppCompatActivity{

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);

        if (savedInstanceState != null) {

            //Save the text of the editText
            bringer = savedInstanceState.getString("bringer");

            input.setText(bringer);

            //Save the Listview
            content = savedInstanceState.getStringArrayList("content");

            adapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, content);

            layout = (ListView) findViewById(R.id.layout);


            layout.setAdapter(adapter);
        }
    }


    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putStringArrayList("content", content);
        outState.putStringArrayList("list", list);

        bringer = input.getText().toString();
        outState.putString("bringer", bringer);
    }

Second Activity:

public class pop extends Activity {

        back.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //Thats where it fails, because it couldnt get the parent-
       view.
                finish();
            }
        });

        sure.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {


            }
        });
    }

}