I first recall reading about so-called "scale colour" or "scale effect" adjustments of model paints in the middle 1980s. It was in Fine Scale Modeler in the USA.
When and where did this topic first come to plastic modelling? In the UK? In the USA?
What was the groundbreaking article on the subject? Did the topic start in the model railroad hobby before reaching the plastic modelling crowd? Who was the benefactor (or culprit, depending on your point of view) who brought it into plastic modelling?