Tkinter:为什么在触摸移动的蓝色矩形时，矩形仍然是黄色的？

import tkinter as tk

class App:
    def __init__(self, root):
        self.root = root
        self.canvas = tk.Canvas(root, width=400, height=400)
        self.canvas.pack()
        
        self.rectangle_id = None
        self.is_blue = False
        
        self.canvas.bind("<Button-1>", self.on_button_press)
        self.canvas.bind("<B1-Motion>", self.on_move_press)
    
    def on_button_press(self, event):
        # 清除之前的矩形
        if self.rectangle_id:
            self.canvas.delete(self.rectangle_id)
        
        # 创建一个新的蓝色矩形
        self.rectangle_id = self.canvas.create_rectangle(event.x - 25, event.y - 25, event.x + 25, event.y + 25, fill="blue")
        self.is_blue = True
    
    def on_move_press(self, event):
        if self.is_blue:
            # 更新矩形的颜色为黄色
            self.canvas.itemconfig(self.rectangle_id, fill="yellow")
            self.is_blue = False
        else:
            # 更新矩形的颜色为蓝色
            self.canvas.itemconfig(self.rectangle_id, fill="blue")
            self.is_blue = True

if __name__ == "__main__":
    root = tk.Tk()
    app = App(root)
    root.mainloop()