library/src/main/java/de/mrapp/android/view/FloatingActionButton.java
private Drawable createDisabledBackgroundDrawable() {
        Drawable drawable = createBackgroundDrawable(getColor());
        Drawable hoverDrawable = createBackgroundDrawable(getDisabledColor());
        return new LayerDrawable(new Drawable[]{drawable, hoverDrawable});
    }
private Drawable createDisabledBackgroundDrawable() {
        Drawable drawable = createBackgroundDrawable(getColor());
        Drawable hoverDrawable = createBackgroundDrawable(getDisabledColor());
        return new LayerDrawable(new Drawable[]{drawable, hoverDrawable});
    }
Creates and returns a drawable, which can be used as the floating action button's background,
when it is disabled.

@return The drawable, which has been created, as an instance of the class {@link Drawable}