protected int makePressColor() {
		int r = (this.backgroundColor >> 16) & 0xFF;
		int g = (this.backgroundColor >> 8) & 0xFF;
		int b = (this.backgroundColor >> 0) & 0xFF;
		r = (r - 30 < 0) ? 0 : r - 30;
		g = (g - 30 < 0) ? 0 : g - 30;
		b = (b - 30 < 0) ? 0 : b - 30;
		return Color.rgb(r, g, b);
	}
Make a dark color to ripple effect

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