@Override
        protected void onDraw(Canvas canvas) {
            super.onDraw(canvas);

            if (numberIndicatorResize == false) {
                LayoutParams params = (LayoutParams) numberIndicator.numberIndicator
                        .getLayoutParams();
                params.height = (int) finalSize * 2;
                params.width = (int) finalSize * 2;
                numberIndicator.numberIndicator.setLayoutParams(params);
            }

            Paint paint = new Paint();
            paint.setAntiAlias(true);
            paint.setColor(backgroundColor);
            if (animate) {
                if (y == 0)
                    y = finalY + finalSize * 2;
                y -= Utils.dpToPx(6, getResources());
                size += Utils.dpToPx(2, getResources());
            }
            canvas.drawCircle(
                    ViewHelper.getX(ball)
                            + Utils.getRelativeLeft((View) ball.getParent())
                            + ball.getWidth() / 2, y, size, paint);
            if (animate && size >= finalSize)
                animate = false;
            if (animate == false) {
                ViewHelper
                        .setX(numberIndicator.numberIndicator,
                                (ViewHelper.getX(ball)
                                        + Utils.getRelativeLeft((View) ball
                                        .getParent()) + ball.getWidth() / 2)
                                        - size);
                ViewHelper.setY(numberIndicator.numberIndicator, y - size);
                numberIndicator.numberIndicator.setText(value + "");
            }

            invalidate();
        }
Make a dark color to press effect

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