I believe it was around 74 or 75. I was in the artillery (2/2 Arty, Fort Sill) at the time. We had red berets.
I was at Ft. Sill in 1972, with that red artillery ascot and a red beret, the dress uniform would look awfully bright.
Here is a mention of the period, and experiment that you are talking about.
“In addition, after HQDA encouraged the unofficial use of morale-enhancing headgear in 1973,”