public void setBackgroundColor(int color) {
		this.backgroundColor = color;
		if (isEnabled())
			beforeBackground = backgroundColor;
		try {
			LayerDrawable layer = (LayerDrawable) getBackground();
			GradientDrawable shape = (GradientDrawable) layer
					.findDrawableByLayerId(R.id.shape_bacground);
			shape.setColor(backgroundColor);
			rippleColor = makePressColor();
		} catch (Exception ex) {
			// Without bacground
		}
	}
Make a dark color to ripple effect

@return
MaterialDesignLibrary/MaterialDesign/src/main/java/com/gc/materialdesign/views/Button.java