Background Color Leaking Through Rounded Border

Question

I am currently trying to make rounded JPanels that are colored, but whenever I set the background, I get an issue. The color is leaking through the border, and I am unsure of how to fix this. I am relatively new to java, and any help would be appreciated. Thanks!

Image of issue:

Image

My code:

import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.*;
import javax.swing.border.Border;

public class Main extends JPanel {

    public static void main(String[] args) {

        JFrame home = new JFrame();
        home.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        home.setLayout(null);
        home.setSize(1000, 700);
        home.setLocation(400, 150);
        home.getContentPane().setBackground(new Color(30, 50, 70));
        home.setResizable(false);

        //UPPER PANEL
        JPanel upper = new JPanel();
        upper.setBackground(new Color(100, 50, 75));
        upper.setBounds(20, 20, 960, 100);
        upper.setBorder(new RoundedBorder(30));

        //LOWER LEFT PANEL
        JPanel ll = new JPanel();
        ll.setBackground(new Color(100, 50, 75));
        ll.setBounds(20, 140, 660, 500);
        ll.setBorder(new RoundedBorder(30));

        //LOWER RIGHT PANEL
        JPanel lr = new JPanel();
        lr.setBackground(new Color(100, 50, 75));
        lr.setBounds(700, 140, 280, 500);
        lr.setBorder(new RoundedBorder(30));

        home.add(ll);
        home.add(lr);
        home.add(upper);
        home.setVisible(true);
    }

    private static class RoundedBorder implements Border {
        private int radius;

        RoundedBorder(int radius) {
            this.radius = radius;
        }

        @Override
        public void paintBorder(Component c, Graphics g, int x, int y, int width, int height) {
            g.drawRoundRect(x, y, width - 1, height - 1, radius, radius);
        }

        @Override
        public Insets getBorderInsets(Component c) {
            return new Insets(this.radius + 1, this.radius + 1, this.radius + 2, this.radius);
        }

        @Override
        public boolean isBorderOpaque() {
            return false;
        }
    }
}

I have tried looking at things about rounded rectangles, but I'm not even sure if I was on the right track.