import javax.swing.*;
import java.awt.*;
class MyGradient extends JFrame {
   JPanel[][] pix = new JPanel[255][255];
   Container con = getContentPane();
   public MyGradient() {
      con.setLayout(new GridLayout(255,255));
      for (int i = 0; i < 255; i++) { for (int j = 0; j < 255; j++) {
         pix[i][j] = new JPanel();
         con.add(pix[i][j]);
      } }
      setSize(255,255);
   }
   public void paint(Graphics gr) {
      super.paint(gr);
      for (int i = 254; i > -1; i--) { for (int j = 254; j > -1; j--) {
         pix[i][j].setBackground(new Color(i, j, i));
      }}
   }
   public static void main(String[] args) { MyGradient aFrame = new MyGradient(); aFrame.setVisible(true); }
}

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