APPLY COLOR IN XML FILE IN ANDROID STUDIO

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/cyan"
    android:orientation="vertical">

    <TextView
        android:layout_width="match_parent"
        android:text="My Activity"
        android:layout_gravity="center"
        android:gravity="center"
        android:textSize="30dp"
        android:textColor="@color/yellow"
        android:background="@color/black"
        android:layout_margin="15dp"
        android:layout_height="wrap_content"></TextView>

    <Button
        android:textColor="@color/white"
        android:layout_width="match_parent"
        android:background="@color/red"
        android:layout_height="wrap_content"
        android:text="Button 1"></Button>

    <Button
        android:textColor="@color/red"
        android:background="@color/CobaltBlue"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Button 2"></Button>
</LinearLayout>