android4.0系统点击后颜色-浅蓝色

android:background="?android:attr/selectableItemBackground"
系统的按钮动作背景
方便查找
顺便复习下？
?[<package_name>:][<resource_type>/]<resource_name>
For example, here's how you can reference an attribute to set the text color to match the "primary" text color of the system theme:
意思是 引用系统定义的theme