Objective -c properties - 无法使用声明的属性更改子视图的颜色

I have a view with a subview whose alpha and backgroundcolor I would like to change through the use of declared properties. I have written some code as below and it works fine to change the alpha, but the background color is not changed when the property is set to a new value. Any help would be appreciated please.I have a view with a subview whose alpha and ba