The first thing one wonders when reading the title is, simply, "Why is the room red in the first place?" The color symbolism behind red can carry many meanings, including rage or love, among others. Red has also been used classically as a symbol for blood or family (see Shakespeare).
So, to answer your question directly, the title "The Red Room" immediately begs a question that the reader must then attempt to resolve. This word choice was a wise one by the author, who undoubtedly wanted to invite readers into this work by using vague simplicity to pique the curiosity of others. Such devices are still used today by contemporary authors who wish to "cause a stir" using their work's title.