Java - Sierpinksi's Triangle

Question

I'm trying to figure out how to draw Sierpinksi's triangle with a pixel limit of 4. Here is my code so far.

import java.awt.*
import java.swing.*

public class SierpTriangle extends Canvas{

    public static void main(String[] args) {    
        JFrame frame = new JFrame("Sierp Triangle");
        frame.setSize(900, 900);
        SierpTriangle st = new SierpTriangle();
        frame.add(st);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);       
    }

    public void paint(Graphics g) {
        drawSTriangle(0, this.getSize().height, this.getSize().height, g);
    }
    
    public void drawSTriangle(int x, int y, int size, Graphics g) {
        int sub = size / 2;
        int[] xPoints = {x, x + size / 2, x + size};
        int[] yPoints = {y, y - size, y};
        g.setColor(Color.BLACK);
        g.fillPolygon(xPoints, yPoints, 3);
        if (sub >= 4) {
            drawSTriangle(x, y, sub, g);//LEFT
            drawSTriangle(x + sub / 2, y - sub, sub, g);//TOP
            drawSTriangle(x + sub, y, sub, g);//RIGHT
        }
    }
}

It seems to show a large grey triangle instead of a Sierpenki's triangle with 4 layers. Can anyone help?