Here is a quote from the Maine Dept. of Agriculture, Conservation & Forestry:
Augusta, ME (September 27, 2017) - The Fall Foliage Report from the Department of Agriculture, Conservation and Forestry reports 70 percent color for the upcoming weekend in northern Maine, while the rest of the state is at 30 to 50 percent color change with low leaf drop throughout the state.
Typically, northern Maine (zones 6 and 7) reaches peak conditions the last week of September into the first week of October. The rest of the state’s progression of color will start occurring from north to south in mid-October. Coastal Maine typically reaches peak conditions mid-to-late October.
“To bring about the intensity of the autumn colors, we look forward to the warm days followed by cool nights. As the days begin to get shorter and the nights longer, the dazzle will soon be visible in central, southern, coastal and western mountains of Maine,” according to Gale Ross, fall foliage spokesperson.