My thinking is those light green paint colors must have been cheaper. I know dark colors cost more and if you leave an old green truck sitting under a tree it just gets greener. Now the trend is "think green" so maybe millenials and yuppies feel better going green.
Green was a very popular period paint color at the time (1971) - think avocado green kitchen appliances.
I've never heard of green periods, until now. I suppose, one too many space ships landed here, in 1971.