Setting background color

styles.xml

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
        <!-- @color is a reference to resource colors.xml -->
        <!-- and 'background' is a name of the resource -->
        <item name="android:windowBackground">@color/background</item>
    </style>

</resources>