I figure the name is a reference to how they're featuring the member colors more now in videos and concerts. A lot of new members for people to learn, especially if they want to recapture mainstream attention. It seems to be working for Momoclo, so...
And with all the new faces, it's easier for fans to link the colors to the members to memorize them. It's smart. If there's gonna be anychange in the title, i think they'll just add "13" to it since every previous album had it's number in the title, but they're not gona change the whole thing (their concert tour is also names after this)