彼の本は赤いです。
His book is red. What is the topic? Is it him or the color red, since 赤い is after the は?
In Japanese, particles come after the things they mark:
彼の本は赤いです。
The topic is the entire phrase 彼の本.
Topic is 彼の本 ("his book") and is clearly marked by the following topic particle は.