Galerinha da Um ajuda, não estou conseguindo mudar a cor de fundo do meu Jframe no netbeans o que fazer? segue o codigo do projeto abaixo:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package ProgressBar;

import javax.swing.JOptionPane;

/**
 *
 * @author abb
 */
public class Login extends javax.swing.JFrame {
    

    /**
     * Creates new form MeuForm
     */
    public Login() {
        initComponents();
    }

    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jButtonEntrar = new javax.swing.JButton();
        jButtonSair = new javax.swing.JButton();
        jCheckBoxLembrarsenha = new javax.swing.JCheckBox();
        user = new javax.swing.JTextField();
        pass = new javax.swing.JPasswordField();
        jLabelNomeUsuario = new javax.swing.JLabel();
        jLabelSenha = new javax.swing.JLabel();
        jLabelNaoconsigoacessar = new javax.swing.JLabel();
        jButtonEsqueciMeulogin = new javax.swing.JButton();
        jLabelJatemcadastro = new javax.swing.JLabel();
        jButtonCadastrese = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setBackground(new java.awt.Color(0, 0, 0));
        setIconImages(null);

        jButtonEntrar.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
        jButtonEntrar.setText("ENTRAR");
        jButtonEntrar.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButtonEntrarActionPerformed(evt);
            }
        });

        jButtonSair.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
        jButtonSair.setText("SAIR");
        jButtonSair.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButtonSairActionPerformed(evt);
            }
        });

        jCheckBoxLembrarsenha.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
        jCheckBoxLembrarsenha.setText("Lembrar senha");

        jLabelNomeUsuario.setFont(new java.awt.Font("Tahoma", 1, 14)); // NOI18N
        jLabelNomeUsuario.setText("Nome do usuário:");

        jLabelSenha.setFont(new java.awt.Font("Tahoma", 1, 14)); // NOI18N
        jLabelSenha.setText("Senha:");

        jLabelNaoconsigoacessar.setFont(new java.awt.Font("Tahoma", 1, 12)); // NOI18N
        jLabelNaoconsigoacessar.setText("Não consigo acessar minha conta, e agora?");

        jButtonEsqueciMeulogin.setFont(new java.awt.Font("Tahoma", 1, 12)); // NOI18N
        jButtonEsqueciMeulogin.setText("ESQUECI MEU LOGIN / SENHA");
        jButtonEsqueciMeulogin.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButtonEsqueciMeuloginActionPerformed(evt);
            }
        });

        jLabelJatemcadastro.setFont(new java.awt.Font("Tahoma", 1, 12)); // NOI18N
        jLabelJatemcadastro.setText("Já tem cadastro na Close Friend? ");

        jButtonCadastrese.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
        jButtonCadastrese.setText("CADASTRAR-SE");
        jButtonCadastrese.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButtonCadastreseActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addComponent(jLabelJatemcadastro, javax.swing.GroupLayout.PREFERRED_SIZE, 213, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addGap(54, 54, 54)
                        .addComponent(jButtonCadastrese, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                        .addContainerGap())
                    .addGroup(layout.createSequentialGroup()
                        .addComponent(jLabelNaoconsigoacessar)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(jButtonEsqueciMeulogin, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                        .addGap(14, 14, 14))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(50, 50, 50)
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addGroup(layout.createSequentialGroup()
                                .addGap(0, 0, Short.MAX_VALUE)
                                .addComponent(jButtonEntrar, javax.swing.GroupLayout.PREFERRED_SIZE, 180, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addGap(26, 26, 26)
                                .addComponent(jButtonSair, javax.swing.GroupLayout.PREFERRED_SIZE, 204, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addGap(64, 64, 64))
                            .addGroup(layout.createSequentialGroup()
                                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                                    .addComponent(jLabelNomeUsuario)
                                    .addComponent(jLabelSenha))
                                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                                    .addComponent(jCheckBoxLembrarsenha)
                                    .addComponent(user, javax.swing.GroupLayout.DEFAULT_SIZE, 307, Short.MAX_VALUE)
                                    .addComponent(pass))
                                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))))))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(26, 26, 26)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(user, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jLabelNomeUsuario, javax.swing.GroupLayout.PREFERRED_SIZE, 24, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(pass, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jLabelSenha, javax.swing.GroupLayout.PREFERRED_SIZE, 20, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(jCheckBoxLembrarsenha)
                .addGap(18, 18, 18)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(jButtonSair)
                    .addComponent(jButtonEntrar))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 42, Short.MAX_VALUE)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jButtonEsqueciMeulogin)
                    .addComponent(jLabelNaoconsigoacessar))
                .addGap(18, 18, 18)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jButtonCadastrese)
                    .addComponent(jLabelJatemcadastro))
                .addGap(45, 45, 45))
        );

        setSize(new java.awt.Dimension(550, 339));
        setLocationRelativeTo(null);
    }// </editor-fold>                        

    private void jButtonEsqueciMeuloginActionPerformed(java.awt.event.ActionEvent evt) {                                                       
        EsqueceuSenha tela = new EsqueceuSenha();
        tela.setVisible(true);
        dispose();
    }                                                      

    private void jButtonSairActionPerformed(java.awt.event.ActionEvent evt) {                                            
        System.exit(0);
    }                                           

    private void jButtonEntrarActionPerformed(java.awt.event.ActionEvent evt) {                                              
        if(user.getText().equals("Admin")&&pass.getText().equals("1234")){
            TelaPrincipal tela = new TelaPrincipal();
            tela.setVisible(true);
            dispose();
        }else{
            JOptionPane.showMessageDialog(rootPane, "Senha ou Usuário Inválidos ! Digite Novamente.");
        }
    }                                             

    private void jButtonCadastreseActionPerformed(java.awt.event.ActionEvent evt) {                                                  
        Registro tela = new Registro();
        tela.setVisible(true);
        dispose();
    }                                                 

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /*
         * Set the Nimbus look and feel
         */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /*
         * If Nimbus (introduced in Java SE 6) is not available, stay with the
         * default look and feel. For details see
         * http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Windows".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(Login.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(Login.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(Login.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(Login.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>
        //</editor-fold>

        /*
         * Create and display the form
         */
        java.awt.EventQueue.invokeLater(new Runnable() {

            public void run() {
                new Login().setVisible(true);
            }
        });
    }
    // Variables declaration - do not modify                     
    private javax.swing.JButton jButtonCadastrese;
    private javax.swing.JButton jButtonEntrar;
    private javax.swing.JButton jButtonEsqueciMeulogin;
    private javax.swing.JButton jButtonSair;
    private javax.swing.JCheckBox jCheckBoxLembrarsenha;
    private javax.swing.JLabel jLabelJatemcadastro;
    private javax.swing.JLabel jLabelNaoconsigoacessar;
    private javax.swing.JLabel jLabelNomeUsuario;
    private javax.swing.JLabel jLabelSenha;
    private javax.swing.JPasswordField pass;
    private javax.swing.JTextField user;
    // End of variables declaration                   
}

@VictorAlves eu também não sei.
Faz o seguinte:
Pegue um jPanel e o extenda pela tela do JFrame.
Ai altere a cor do JPanel.
Pelo menos vair ser um início, até surgir uma resposta mais adequada.