Floating action button background color change.

The background color of this view defaults to the your theme's colorAccent. If you wish to change this at runtime then you can do so via setBackgroundTintList(ColorStateList).

<com.google.android.material.floatingactionbutton.FloatingActionButton
    android:id="@+id/"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:backgroundTint="@android:color/holo_orange_dark"
    />

or

fb.setBackgroundTintList(ColorStateList.valueOf(your color in int));

stackoverflow