In themes.xml:

<style name="AppTheme" parent="Theme.AppCompat">
    <!-- Theme attributes here -->
</style>

In AndroidManifest.xml:

<application
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme">
    
    <!-- Activity declarations here -->

</application>

You can customize your theme’s color palette.

Using framework APIs

<style name="AppTheme" parent="Theme.Material">
    <item name="android:colorPrimary">@color/primary</item>
    <item name="android:colorPrimaryDark">@color/primary_dark</item>
    <item name="android:colorAccent">@color/accent</item>
</style>

Using the Appcompat support library (and AppCompatActivity)

<style name="AppTheme" parent="Theme.AppCompat">
    <item name="colorPrimary">@color/primary</item>
    <item name="colorPrimaryDark">@color/primary_dark</item>
    <item name="colorAccent">@color/accent</item>
</style>

In themes.xml:

<style name="MyActivityTheme" parent="Theme.AppCompat">
    <!-- Theme attributes here -->
</style>

In AndroidManifest.xml:

<application
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/Theme.AppCompat">
    
    <activity
        android:name=".MyActivity"
        android:theme="@style/MyActivityTheme" />

</application>

<style name="AppTheme" parent="Theme.AppCompat">
    <item name="android:colorEdgeEffect">@color/my_color</item>
</style>

This attribute can change the background of the Status Bar icons (at the top of the screen) to white.

<style name="AppTheme" parent="Theme.AppCompat">
    <item name="android:windowLightStatusBar">true</item>
</style>

The navigation bar (at the bottom of the screen) can be transparent. Here is the way to achieve it.

<style name="AppTheme" parent="Theme.AppCompat">
    <item name="android:windowTranslucentNavigation">true</item>
</style>

The Status Bar (top of the screen) can be made transparent, by applying this attribute to the style:

<style name="AppTheme" parent="Theme.AppCompat">
    <item name="android:windowTranslucentStatus">true</item>
</style>

When defining themes, one usually uses the theme provided by the system, and then changes modifies the look to fit his own application. For example, this is how the Theme.AppCompat theme is inherited:

<style name="AppTheme" parent="Theme.AppCompat">
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
</style>

This theme now has all the properties of the standard Theme.AppCompat theme, except the ones we explicitly changed.

There is also a shortcut when inheriting, usually used when one inherits from his own theme:

<style name="AppTheme.Red">
    <item name="colorAccent">@color/red</item>
</style>

Since it already has AppTheme. in the start of it's name, it automatically inherits it, without needing to define the parent theme. This is useful when you need to create specific styles for a part (for example, a single Activity) of your app.

Using more than one theme in your Android application, you can add custom colors to every theme, to be like this:

First, we have to add our themes to style.xml like this:

<style name="OneTheme" parent="Theme.AppCompat.Light.DarkActionBar">

</style>

<!--  -->
<style name="TwoTheme" parent="Theme.AppCompat.Light.DarkActionBar" >

</style>
......

Above you can see OneTheme and TwoTheme.

Now, go to your AndroidManifest.xml and add this line: android:theme="@style/OneTheme" to your application tag, this will make OneTheme the default theme:

<application
        android:theme="@style/OneTheme"
        ...>

Create new xml file named attrs.xml and add this code :

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <attr name="custom_red" format="color" />
    <attr name="custom_blue" format="color" />
    <attr name="custom_green" format="color" />
</resources>
<!-- add all colors you need (just color's name) -->

Go back to style.xml and add these colors with its values for each theme :

<style name="OneTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <item name="custom_red">#8b030c</item>
    <item name="custom_blue">#0f1b8b</item>
    <item name="custom_green">#1c7806</item>
</style>

<style name="TwoTheme" parent="Theme.AppCompat.Light.DarkActionBar" >
    <item name="custom_red">#ff606b</item>
    <item name="custom_blue">#99cfff</item>
    <item name="custom_green">#62e642</item>
</style>

Now you have custom colors for each theme, let's add these color to our views.

Add custom_blue color to the TextView by using "?attr/" :

Go to your imageView and add this color :

<TextView>
    android:id="@+id/txte_view"
    android:textColor="?attr/custom_blue" />

Mow we can change the theme just by single line setTheme(R.style.TwoTheme); this line must be before setContentView() method in onCreate() method, like this Activity.java :

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setTheme(R.style.TwoTheme);
    setContentView(R.layout.main_activity);
    ....
}

change theme for all activities at once

If we want to change the theme for all activities, we have to create new class named MyActivity extends AppCompatActivity class (or Activity class) and add line setTheme(R.style.TwoTheme); to onCreate() method:

public class MyActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (new MySettings(this).isDarkTheme())
            setTheme(R.style.TwoTheme);
    }
}

Finally, go to all your activities add make all of them extend the MyActivity base class:

public class MainActivity extends MyActivity {
    ....
}

In order to change the theme, just go to MyActivity and change R.style.TwoTheme to your theme (R.style.OneTheme , R.style.ThreeTheme ....).