RadioButton changes background color

quizapp.java

package com.example.android.quizapp;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;
import android.widget.RadioButton;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    public void onSelect(View view) {

        RadioButton bgRadioButton1 = (RadioButton) findViewById(R.id.q1_answer1);
        boolean isRadioButton1Selected = bgRadioButton1.isChecked();
        RadioButton bgRadioButton2 = (RadioButton) findViewById(R.id.q1_answer2);
        boolean isRadioButton2Selected = bgRadioButton2.isChecked();
        RadioButton bgRadioButton3 = (RadioButton) findViewById(R.id.q1_answer3);
        boolean isRadioButton3Selected = bgRadioButton3.isChecked();
        RadioButton bgRadioButton4 = (RadioButton) findViewById(R.id.q1_answer4);
        boolean isRadioButton4Selected = bgRadioButton4.isChecked();


        // Is the button now checked?
        boolean checked = ((RadioButton) view).isChecked();

        // Check which radio button was clicked
        switch (view.getId()) {
            case R.id.q1_answer1:
                if (checked)
                bgRadioButton1.setBackgroundColor(getResources().getColor(R.color.radio_bg));
                bgRadioButton2.setBackgroundColor(getResources().getColor(R.color.main_bg));
                bgRadioButton3.setBackgroundColor(getResources().getColor(R.color.main_bg));
                bgRadioButton4.setBackgroundColor(getResources().getColor(R.color.main_bg));

                break;
            case R.id.q1_answer2:
                if (checked)
                bgRadioButton1.setBackgroundColor(getResources().getColor(R.color.main_bg));
                bgRadioButton2.setBackgroundColor(getResources().getColor(R.color.radio_bg));
                bgRadioButton3.setBackgroundColor(getResources().getColor(R.color.main_bg));
                bgRadioButton4.setBackgroundColor(getResources().getColor(R.color.main_bg));
                break;
            case R.id.q1_answer3:
                if (checked)
                bgRadioButton1.setBackgroundColor(getResources().getColor(R.color.main_bg));
                bgRadioButton2.setBackgroundColor(getResources().getColor(R.color.main_bg));
                bgRadioButton3.setBackgroundColor(getResources().getColor(R.color.radio_bg));
                bgRadioButton4.setBackgroundColor(getResources().getColor(R.color.main_bg));
                break;
            case R.id.q1_answer4:
                if (checked)
                bgRadioButton1.setBackgroundColor(getResources().getColor(R.color.main_bg));
                bgRadioButton2.setBackgroundColor(getResources().getColor(R.color.main_bg));
                bgRadioButton3.setBackgroundColor(getResources().getColor(R.color.main_bg));
                bgRadioButton4.setBackgroundColor(getResources().getColor(R.color.radio_bg));
                break;
        }
    }
}