If you’re using AndroidX, to change the color of the icon you must use app:tint opposed to android:tint
<com.google.android.material.floatingactionbutton.FloatingActionButton
style="@style/Widget.MaterialComponents.FloatingActionButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="16dp"
android:layout_marginBottom="16dp"
app:backgroundTint="@color/colorPrimary"
app:tint="@color/white"
app:srcCompat="@drawable/ic_add"
/>