"All buildings have secrets to reveal, it seems. [...] Whether you're investigating paint or doing conservation testing, the idea is to try to understand what things are made out of, what the pathologies are, the layers sequence - and they can reveal quite a bit of information. It's about the relationship of all these finishes one to another, and their history: history of deterioration, history of change." - Jeff Greene
It's hard to be a preservationist and not hear the words "original paint colors" at least once every couple months. But while the concept itself may be easy to understand, the process of identifying those colors and finishes is much more involved (think scalpels and microscopes).
Check out this great video produced by EverGreene Architectural Arts on the practice of original finish investigation: