try adding this or you can use [Materials][1]
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="end|bottom"
android:src="@drawable/ic_my_icon"
android:layout_margin="16dp" />
[1]: https://material.io/develop/android/components/floating-action-button/
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
app:elevation="6dp"
app:backgroundTint="@color/colorAccent"
app:pressedTranslationZ="12dp"
android:layout_margin="@dimen/fab_margin"
android:src="@drawable/add"/>
Note that you add colors in res/values/color.xml
and include the attribute in your fab
app:backgroundTint="@color/addedColor"
