There was an interesting article in National Geographic in the 1970s about a 50 foot high mound that was a village site. Upon excavating they found it went back either 6,000 years or 6,000 BC (can’t remember which). The early pottery was colorful and imaginative, then 2 or 3,000 years later there was pottery that was well made, but drab and monocolor. I think the mound was in Bulgaria. I remember thinking, “what happened to destroy these people’s joy and creativity?”
Gobekli Tepe: The World’s First Temple? ( massive carved stones about 11,000 years old )
Smithsonian magazine ^ | November 2008 | # Andrew Curry # Photographs by Berthold Steinhilber
http://www.freerepublic.com/focus/news/2130449/posts
Was this what you remember?
Maybe they just ran out of colored paint. ;’) Probably there was a disaster, invasion, plague, population change.