JPanel background is not visible

Initially I was grabbing a chess but I ran into this problem so I simplified the program to ask the question.

The Program in question is the following:

public class NewClass {
public static void main(String[] args)  {
     javax.swing.SwingUtilities.invokeLater(() -> {
         JFrame F = new JFrame("Program");
         F.setSize(600,600);
         F.setLayout(null);
         tab t = new tab();
         F.add(t);
         t.addLabel(0,new Pawn());
         F.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         F.setVisible(true);
     });
    }
}

class tab extends JPanel
{
    JPanel[] squares;
    public tab ()
    {
        squares = new JPanel[4];
        setBackground(Color.black);
        setBounds(20,20,80,80);
        setBorder(BorderFactory.createLineBorder(Color.black, 2));
        GridLayout l = new GridLayout(2,2);
        l.setHgap(3);
        l.setVgap(3);
        setLayout(l);
        for(int i = 0 ; i< 4;i++)
        {
            squares[i] = new JPanel();
            squares[i].setBackground(Color.white);
            squares[i].setLayout(new BorderLayout());
            squares[i].setOpaque(true);
            add(squares[i]);
        }   
   } 
    public void addLabel(int s,JLabel l)
    {
        squares[s].add(l);
    }
}

class Pawn extends JLabel
{
    public Pawn() {
         ImageIcon im = new ImageIcon("/home/jose/Escritorio/pb.png");
         this.setIcon(im);
         setOpaque(true);
         setBackground(new Color(100,200,50,0));
      }
 }

The Program creates a JPanel (through the tab class) that inside has another 4 JPanel and simulates a 2x2 board, then tab has the addLabel function that allows me to add a peon.

The problem in question occurs when I add these 2 lines of code to the peon

    setOpaque(true);
    setBackground(new Color(100,200,50,0));

The 2 lines should make the label transparent (for the fourth Color parameter), but apart from that, it also prevents squares [0] from showing its background, showing instead the background of the JPanel container .