Python学习，根据书《Python编程：从入门到实践》学习，为啥不变颜色，理论上应该是灰色，但是它不变色，是黑色

```import pygame
def run_game():
    pygame.init()
    pygame.display.set_caption("Alien Invasion")
    screen = pygame.display.set_mode((1200,800))
    bg_color = (230, 230, 230)
    while True:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                sys.exit()
                screen.fill(bg_color)
                pygame.display.flip()
run_game()

你打错了！代码缩进有问题

import pygame
def run_game():
    pygame.init()
    pygame.display.set_caption("Alien Invasion")
    screen = pygame.display.set_mode((1200,800))
    bg_color = (230, 230, 230)
    while True:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                sys.exit()
        screen.fill(bg_color)
        pygame.display.flip()
'''
上面这两行缩进出问题了
'''
run_game()