What do green Massachusetts license plates mean?

Question

I recently got back from a vacation to Cape Cod and I was wondering why there are some green Mass license plates but mostly red. My conclusion was that the green ones meant you lived in Cape Cod and the red meant you lived in Mass. Can anyone tell me whether this is true or not?

Answer 1

Massachusetts first issued green lettered plates with 2 year staggered registration  in March 1977.  They still had unissued red letter plates on hand so on alternating weeks they went back and forth until the red letter plate supply was exhausted in Spring 1978. The green letter plates ALSO were issued in all numeric format 1 to 999,999.  Numbers 1-99,999 are reserved numbers Numbers 100,000 to 999,999 are generic. (Again thanks to Rich Bell!) Many of these are still actively registered today!

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http://www.w-a.com/maplate.htm

Lots of pictures and info here!