Android : Need help in chaning text color in android app

In the below code, how would i change it so i can make the font color black? This is driving me crazy. please help!

  <?xml version="1.0" encoding="UTF-8"?>
   <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" >
 <PreferenceCategory
     android:icon="@drawable/ic_settings_bluetooth"
    android:title="@string/settings_bluetooth" >
    <SwitchPreference
        android:defaultValue="true"
                       android:fragment="no.nordicsemi.android.nrftemp.fragment.SettingsFragmetn$BluetoothSettingsFragment"
        android:key="settings_scan_in_background"
        android:summary="@string/settings_scan_in_background_summary"
        android:title="@string/settings_scan_in_background_title"/>

    <ListPreference
        android:dependency="settings_scan_in_background"
        android:entries="@array/settings_periods"
        android:entryValues="@array/settings_periods_values"
        android:key="settings_scan_interval"
        android:defaultValue="300000"
        android:title="@string/settings_scan_period_title" />
</PreferenceCategory>
<PreferenceCategory android:title="@string/settings_about" >
    <no.nordicsemi.android.nrftemp.fragment.AboutPreference android:title="@string/settings_about_title" />
</PreferenceCategory>