用VC做一个背景颜色改变。前两秒黑屏，t=2s时出现红色方块，显示1s后消失，然后是0.5s的黑屏，出现绿色方块，显示1s-Using VC to be a background color changes. Two seconds before the black screen, t = 2s when the red box shows disappear after 1s, then the 0.5s in the black, green box appears, showing 1s