It does decline super fast. You'll be absolutely blown away one day, and literally 48 hours later it'll be all orange and faded with decent leaf drop. It'll go from all colors to all orange mixed with stick season very fast.
The thing with "best color" will depend on if you prefer to have some green still mixed in, then it's definitely the last week of September. If you want no green and only yellow/orange/red then "peak" is probably in October, even there in Randolph. The great thing about foliage season is as it starts going, you'll have days where you are like wow, this is awesome what could be better. Then a couple days later you are like holy shit this is awesome, does it get better? And you'll do that until all the sudden you wake up one day and its over in a snap of the fingers.