One thing I noticed in the last few weeks is the excitement with a lot of people on the internet about working from B/W and adding color later on.
I learned this from Bobby Chiu as well, and I have to say that I immediately started working with this, but I did it the other way around, because I never got the colors right after adding them to a B/W image. Instead, I use(d) it to check the values of the colored image. In my opinion the only reason to start in B/W; Because of the values.
The values of your original B/W image are different from the colored image (I prefer to check values of your colored image by adding a black layer on top and the blend mode on color, instead of turning the saturation down). Just check it yourself.
Experimenting with technical theories is what you should do. Understand them. Don't expect these kind of trics to do the magic for you. Make it work.