如何在python kivy文件中制作我的自定义widget，并通过更改其大小、位置和颜色来多次使用它？

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.graphics import Color, Rectangle

class MyWidget(Widget):
    pass

class MyWidget(Widget):
    def change_color(self, color):
        self.canvas.clear()
        with self.canvas:
            Color(*color)
            Rectangle(pos=self.pos, size=self.size)

<MyWidget>:
    canvas:
        Color:
            rgba: 1, 0, 0, 1  # 设置初始颜色为红色
        Rectangle:
            pos: self.pos
            size: self.size

class MyApp(App):
    def build(self):
        return MyWidget()

if __name__ == '__main__':
    MyApp().run()

class MyApp(App):
    def build(self):
        widget1 = MyWidget()
        widget1.change_color((1, 0, 0, 1))  # 设置颜色为红色

        widget2 = MyWidget()
        widget2.change_color((0, 1, 0, 1))  # 设置颜色为绿色

        return widget1, widget2