这两组的区别：The boy in blue is my brother.是简单句,而The boy who is in blue is my brother.则是复合句,其中who is in blue 是定语从句,修饰boy.
The book written by my father is my favorite.简单句,其中written by my father不是介词短语,而是过去分词短语作定语,修饰book；The book which is written by my father is my favorite.复合句