Here's an example of how to create a custom renderer for the column headers of a JTable in Java:

import java.awt.Component;
import java.awt.Font;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.table.DefaultTableCellRenderer;
import javax.swing.table.JTableHeader;
import javax.swing.table.TableColumnModel;
import javax.swing.table.TableModel;

public class CustomTableHeaderRendererExample extends JFrame {

    public CustomTableHeaderRendererExample() {
        super("Custom Table Header Renderer Example");

        // Create the table model
        Object[][] data = {
                {"John Doe", "25", "Male"},
                {"Jane Smith", "30", "Female"},
                {"Bob Johnson", "40", "Male"}
        };
        String[] columnNames = {"Name", "Age", "Gender"};
        TableModel tableModel = new CustomTableModel(data, columnNames);

        // Create the table
        JTable table = new JTable(tableModel);

        // Set the column header renderer
        TableColumnModel columnModel = table.getColumnModel();
        for (int i = 0; i < columnModel.getColumnCount(); i++) {
            columnModel.getColumn(i).setHeaderRenderer(new CustomTableHeaderRenderer());
        }

        // Add the table to a scroll pane
        JScrollPane scrollPane = new JScrollPane(table);
        add(scrollPane);

        // Set the size, location and visibility of the frame
        pack();
        setLocationRelativeTo(null);
        setVisible(true);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {
        new CustomTableHeaderRendererExample();
    }

    // Custom table model
    private static class CustomTableModel extends javax.swing.table.DefaultTableModel {

        public CustomTableModel(Object[][] data, String[] columnNames) {
            super(data, columnNames);
        }

        // Disable cell editing
        @Override
        public boolean isCellEditable(int row, int column) {
            return false;
        }
    }

    // Custom table header renderer
    private static class CustomTableHeaderRenderer extends DefaultTableCellRenderer {

        public Component getTableCellRendererComponent(JTable table, Object value, boolean isSelected, boolean hasFocus, int row, int column) {
            super.getTableCellRendererComponent(table, value, isSelected, hasFocus, row, column);

            // Set the font, background and foreground color of the header
            setFont(new Font("Arial", Font.BOLD, 14));
            setBackground(table.getTableHeader().getBackground());
            setForeground(table.getTableHeader().getForeground());

            return this;
        }
    }
}

In this example, we create a custom CustomTableHeaderRenderer class that extends DefaultTableCellRenderer and overrides the getTableCellRendererComponent() method. This method is called by the JTableHeader to render the column headers.

In the getTableCellRendererComponent() method, we set the font, background color and foreground color of the header using the setFont(), setBackground() and setForeground() methods. We also call the super.getTableCellRendererComponent() method to perform any default rendering.

In the CustomTableModel class, we extend DefaultTableModel and override the isCellEditable() method to disable cell editing.

In the CustomTableHeaderRendererExample class, we create a JTable with a custom table model and set the column header renderer to a new instance of CustomTableHeaderRenderer. We then add the JTable to a JScrollPane and add the scroll pane to the frame.

When you run this example, you'll see a JTable with column headers that have a custom font and color.