I never really liked adult colouring books, the outlines are already done for you, there's no room to do any drawing. I hope tracing books will become a thing in the future, but one thing I would warn a publisher of is that it's very difficult to find the right levels of grey in print. I made this as a personal mental health project and to give me the confidence to get back into Jiu Jitsu after some years. Then it occurred to me that others might be in this position too, or similar, and now it is my goal to share it.