The 1st year Wife, daughter, and myself went to Maine was in August. Too crowded and no colors either. We did go on a whale watching boat and saw them. Really neat.
Went up to Moosehead Lake to look for Moose and saw quite a few. They are awesome also.
The next several years we went up there, we went in late September or the 2nd & 3rd weeks of October. Not as crowded, but some shops close up in early October.
We stayed close to the coast from "up North to down South". Wife and daughter liked going antique shopping, or shopping in general, and I was alway able to find a brew pub to relax and enjoy myself. Ate lots of Lobstah, Oysters, New England Clam Chowdah, etc., etc..
We always had a good time, except for one year we went out whale watching and the seas were rough. Probably half the boat passengers got sea sick, including my Wife and daughter. Captain pulled the plug and brought us back to the dock oin Bar Harbor. They also refunded us our money for the trip.