To create my Washi tape journal, I divided the journal into 2 sections, but set and by color. This was particularly useful for me, as I tend to like purchasing sets of washi tape, and I store them together in those sets, so by having them organized so that I can see what the set is, and the tapes that are in it, I can more easily pull those sets to use. And, when I run out of these, the sets are labeled, so that I know what I need to replace.
The back half of my book is arranged by color, which is where my loose washi tapes are organized. I tend toward neutrals, so there are many more grey than any other color, and for some reason, I have a lot of gold.