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.argb(70, r, g, b);
    }
Make a dark color to press effect

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