Breck shampoo was still really popular in the 1970s, but they did seem to capture the zeitgeist of the times with their ‘natural’ focus. Gold Formula Breck supposedly had far less detergent, and far more ‘natural’ ingredients. It was intended to get out the dirt, but leave the ‘natural’ shine.
I used Breck shampoo religiously in the 60s and 70s. I always used the ‘O’ version (for oily hair), and washed it every day. My hair always did look great!