With having so many workbooks inside desks, I just swipe a fat Mr. Sketch marker along the bottom pages of the book. That way, when the books are piled inside their desks, they can see the colors! When I ask my students to take out a book, I'll say something like, "Please take out your Grammar Green book!" It really does help, and it makes transitions quicker and easier! And after a few weeks, my kiddos will be telling me which book is which!