Manipulando JComboBox

//Crie os 6 combobox no seu form e deixe-os sem conteúdo algum. Na inicialização do form adicione os ítens aos combos, adicione tudo em todos:
        jComboBox1.addItem("UM");
        jComboBox1.addItem("DOIS");
        jComboBox1.addItem("TRES");
        jComboBox1.addItem("QUATRO");
        jComboBox1.addItem("CINCO");
        jComboBox1.addItem("SEIS");
        
        jComboBox2.addItem("UM");
        jComboBox2.addItem("DOIS");
        jComboBox2.addItem("TRES");
        jComboBox2.addItem("QUATRO");
        jComboBox2.addItem("CINCO");
        jComboBox2.addItem("SEIS");  

//Deixe todos os combos como enable false, menos o primeiro.
//Na ActionPerformed do primeiro combo coloque:

    private void jComboBox1ActionPerformed(java.awt.event.ActionEvent evt) {                                           
        jComboBox2.enable(true);
        jComboBox2.removeItem(jComboBox1.getSelectedItem());
        jComboBox3.removeItem(jComboBox1.getSelectedItem());
        jComboBox4.removeItem(jComboBox1.getSelectedItem());
        jComboBox5.removeItem(jComboBox1.getSelectedItem());
        jComboBox6.removeItem(jComboBox1.getSelectedItem());
    }  
//Repita para os demais Combos
    private void jComboBox2ActionPerformed(java.awt.event.ActionEvent evt) {                                           
        jComboBox3.enable(true);
        jComboBox3.removeItem(jComboBox2.getSelectedItem());
        jComboBox4.removeItem(jComboBox2.getSelectedItem());
        jComboBox5.removeItem(jComboBox2.getSelectedItem());
        jComboBox6.removeItem(jComboBox2.getSelectedItem());
    }

package tmp;

import java.awt.Color;
import java.awt.Component;
import java.awt.event.ActionListener;

import javax.swing.ComboBoxEditor;
import javax.swing.DefaultListCellRenderer;
import javax.swing.JComboBox;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.event.EventListenerList;

public class JComboBoxColor extends JComboBox {

    /**
     * Renderer
     */
    private class ColorCellRenderer extends DefaultListCellRenderer {
        @Override
        public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected,
                boolean cellHasFocus) {

            Component c = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);

            if (value instanceof Color) {
                c.setBackground((Color) value);
                c.setForeground((Color) value);
            }

            return c;
        }
    }

    /**
     * Editor
     */
    private class ColorCellEditor implements ComboBoxEditor {
        private JLabel component = new JLabel();
        private Object value = null;
        transient protected EventListenerList listenerList = new EventListenerList();

        public Component getEditorComponent() {
            if (getItem() instanceof Color) {
                component.setBackground((Color) getItem());
                component.setForeground((Color) getItem());
            }
            component.setText("");
            component.setOpaque(true);
            return component;
        }

        public Object getItem() {
            return this.value;
        }

        public void setItem(Object value) {
            if (value instanceof Color) {
                component.setBackground((Color) value);
                component.setForeground((Color) value);
            }
            this.value = value;
        }

        public void addActionListener(ActionListener l) {
            listenerList.add(ActionListener.class, l);
        }

        public void removeActionListener(ActionListener l) {
            listenerList.remove(ActionListener.class, l);
        }

        public void selectAll() {
        }
    }

    /**
     * Contructor
     */
    public JComboBoxColor() {
        setRenderer(new ColorCellRenderer());
        setEditor(new ColorCellEditor());
        setEditable(true);
    }
}

cbPerfil.addItem(new Color(255, 0, 0));
//Depois de setar todas as opções do JComboBox vc renderiza ele usando a classe abaixo.
cbPerfil.setRenderer(new ColorComboRenderer());

import java.awt.Color;
import java.awt.Component;
import java.awt.Graphics;

import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.ListCellRenderer;

public class ColorComboRenderer extends JPanel implements ListCellRenderer {
  protected Color m_c = Color.black;

  public ColorComboRenderer() {
    super();
  }

  public Component getListCellRendererComponent(JList list, Object obj,
      int row, boolean sel, boolean hasFocus) {
    if (obj instanceof Color)
      m_c = (Color) obj;
    return this;
  }

    @Override
  public void paint(Graphics g) {
    setBackground(m_c);
    super.paint(g);
  }
}