Source code for https://victorfont.com/simple-advanced-lesson-android-programming-changing-tabwidget-tab-colors/

android_open_source_code.xml

<!-- Copyright (C) 2008 The Android Open Source Project

     Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.
     You may obtain a copy of the License at

          <a href="http://www.apache.org/licenses/LICENSE-2.0">http://www.apache.org/licenses/LICENSE-2.0</a>

     Unless required by applicable law or agreed to in writing, software
     distributed under the License is distributed on an "AS IS" BASIS,
     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
     implied. See the License for the specific language governing
     permissions and limitations under the License.
-->

<selector xmlns:android="<a href="http://schemas.android.com/apk/res/android">http://schemas.android.com/apk/res/android</a>">
    <!-- Non focused states -->
    <item android:state_focused="false" android:state_selected="false"
        android:state_pressed="false"
        android:drawable="@drawable/tab_unselected_v4" />
    <item android:state_focused="false" android:state_selected="true"
        android:state_pressed="false"
        android:drawable="@drawable/tab_selected_v4" />

    <!-- Focused states -->
    <item android:state_focused="true" android:state_selected="false"
        android:state_pressed="false"
        android:drawable="@drawable/tab_focus" />
    <item android:state_focused="true" android:state_selected="true"
        android:state_pressed="false"
        android:drawable="@drawable/tab_focus" />

    <!-- Pressed -->
    <item android:state_pressed="true"
        android:drawable="@drawable/tab_press" />
</selector>

set_tab_colors.java

protected void setTabColors() {

  /**
   * Before we do anything, determine saved value of IsLightColors
   */
  MyApp app = (MyApp) this.getApplication();
  IsLightColors = app.RetrieveBoolean(getString(R.string.LightColorsKey));

  // set the color scheme and resource based on IsLightColors user prefs
  int tab_indicator = IsLightColors ? R.drawable.tab_indicator_v4_light : R.drawable.tab_indicator_v4;
  int layoutColor = IsLightColors ? Color.WHITE : Color.BLACK;

  View myLayout = findViewById(R.id.main_layout);
  myLayout.setBackgroundColor(layoutColor);
  // set the background resource for each tab
  for (int i = 0; i < tabHost.getTabWidget().getChildCount(); i++) {
    tabHost.getTabWidget().getChildAt(i).setBackgroundResource(tab_indicator);
  }

 }