protected void setAttributes(AttributeSet attrs) {

        setBackgroundResource(R.drawable.background_transparent);

        // Set size of view
        setMinimumHeight(Utils.dpToPx(48, getResources()));
        setMinimumWidth(Utils.dpToPx(80, getResources()));

        // Set background Color
        // Color by resource
        int bacgroundColor = attrs.getAttributeResourceValue(ANDROIDXML,
                "background", -1);
        if (bacgroundColor != -1) {
            setBackgroundColor(getResources().getColor(bacgroundColor));
        } else {
            // Color by hexadecimal
            int background = attrs.getAttributeIntValue(ANDROIDXML, "background", -1);
            if (background != -1)
                setBackgroundColor(background);
        }

        showNumberIndicator = attrs.getAttributeBooleanValue(MATERIALDESIGNXML,
                "showNumberIndicator", false);
        min = attrs.getAttributeIntValue(MATERIALDESIGNXML, "min", 0);
        max = attrs.getAttributeIntValue(MATERIALDESIGNXML, "max", 0);
        value = attrs.getAttributeIntValue(MATERIALDESIGNXML, "value", min);

        ball = new Ball(getContext());
        RelativeLayout.LayoutParams params = new LayoutParams(Utils.dpToPx(20,
                getResources()), Utils.dpToPx(20, getResources()));
        params.addRule(RelativeLayout.CENTER_VERTICAL, RelativeLayout.TRUE);
        ball.setLayoutParams(params);
        addView(ball);

        // Set if slider content number indicator
        // TODO
        if (showNumberIndicator) {
            numberIndicator = new NumberIndicator(getContext());
        }

    }
Make a dark color to press effect

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