The style has no selector: using one will either break the build/runtime or will have no effect and be neglected. There are only two types of selectors: for colors and for drawables.
So, there is only one option: apply bold style on the fly, possibly, by listening to check state changes.
=== Example ===
MainActivity.java:
package com.example.radiobuttontest;
import android.os.Bundle;
import android.app.Activity;
import android.graphics.Typeface;
import android.widget.CompoundButton;
import android.widget.RadioButton;
import android.widget.RadioGroup;
public class MainActivity extends Activity implements CompoundButton.OnCheckedChangeListener {
private RadioGroup mGroup2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mGroup2 = (RadioGroup)findViewById(R.id.radioGroup2);
RadioButton button1 = (RadioButton)findViewById(R.id.option_1);
button1.setOnCheckedChangeListener(this);
}
@Override
protected void onResume() {
super.onResume();
RadioButton checked = (RadioButton)findViewById(mGroup2.getCheckedRadioButtonId());
checked.setTypeface(Typeface.DEFAULT_BOLD);
}
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
buttonView.setTypeface(isChecked ? Typeface.DEFAULT_BOLD : Typeface.DEFAULT);
}
}
layout/activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<RadioGroup xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/radioGroup2"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<RadioButton
android:id="@+id/option_1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:checked="true"
android:text="@string/option_1"
android:textColor="@drawable/radio_picker_color" />
<RadioButton
android:id="@+id/option_2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/option_2"
android:textColor="@drawable/radio_picker_color" />
</RadioGroup>
drawable/radio_picker_color.xml [I changed colors you have used (they are very faint) in the question with "#0099CC" for demonstration purposes]:
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<!-- checked -->
<item android:state_checked="true"
android:color="#0099CC" />
<!-- default -->
<item android:color="#0099CC" />
</selector>
Result:
Hope this helps.