PyQt5:为什么我只能对QTableWidget单元格使用两种颜色？

from PyQt5.QtWidgets import QApplication, QTableWidget, QTableWidgetItem, QWidget, QVBoxLayout
from PyQt5.QtGui import QColor

class CustomTableWidgetItem(QTableWidgetItem):
    def __init__(self, text, background_color, foreground_color):
        super().__init__(text)
        self.background_color = background_color
        self.foreground_color = foreground_color

    def paint(self, painter, option, index):
        painter.fillRect(option.rect, self.background_color)
        painter.setPen(self.foreground_color)
        painter.drawText(option.rect, self.text())

app = QApplication([])
window = QWidget()
layout = QVBoxLayout()
table_widget = QTableWidget(3, 3)
table_widget.setHorizontalHeaderLabels(['Column 1', 'Column 2', 'Column 3'])

# 创建自定义的QTableWidgetItem，并设置不同的背景色和前景色
item1 = CustomTableWidgetItem('Item 1', QColor(255, 0, 0), QColor(255, 255, 255))
item2 = CustomTableWidgetItem('Item 2', QColor(0, 255, 0), QColor(0, 0, 0))
item3 = CustomTableWidgetItem('Item 3', QColor(0, 0, 255), QColor(255, 255, 255))

# 将自定义的QTableWidgetItem添加到QTableWidget中
table_widget.setItem(0, 0, item1)
table_widget.setItem(0, 1, item2)
table_widget.setItem(0, 2, item3)

layout.addWidget(table_widget)
window.setLayout(layout)
window.show()
app.exec_()