what makes fall colors?

here's what Howard Sheckter - Sierra Nevada weather guru - reminds us as autumn closes in on the high country. The rest of his current forecast is here.

"THERE IS MORE GOLD COLOR SHOWING UP WITHIN THE GREEN IN THE HIGH COUNTRY AS OF LATE.....THIS IS DUE TO A STRETCH OF SOME CHILLY NIGHTS THAT IN SOME CASES HAS CAUSED NIGHT TIME LOWS DOWN INTO THE LOW 30S AND EVEN UPPER TWENTIES IN THE BACK COUNTRY......THE VERY DRY AIR AND ITS VERY LOW DEWPOINTS ALLOWS NIGHT TIME TEMPERATURES TO FALL TO SOME PRETTY CHILLY LEVELS...ESPECIALLY IN THE WIND PROTECTED AREAS. THE TIMING OF COLOR OR THE DEGREE OF COLOR IN THE HIGH COUNTRY DOES NOT HAVE ANY RELATIONSHIP TO...WHAT'S TO COME WX WISE OR ANY FORECASTING ABILITIES OF THE FUTURE....RATHER WHAT HAS ALREADY HAPPENED. THE SIMPLE CAUSES OF COLOR CHANGE IN THE FALL LEAVES IS CREATED "IN PART" BY THE ABSENCE OF, OR THE MASKING EFFECTS OF CHLOROPHYLL...SEE BELOW:

The green pigment in leaves is chlorophyll. Chlorophyll absorbs red and blue light from the sunlight that falls on leaves. Therefore, the light reflected by the leaves is diminished in red and blue and appears green. Chlorophyll is not a very stable compound; bright sunlight causes it to decompose. To maintain the amount of chlorophyll in their leaves, plants continuously synthesize it. The synthesis of chlorophyll in plants requires sunlight and WARM temperatures. Therefore, during summer, chlorophyll is continuously broken down and regenerated in the leaves of trees.

The range and intensity of autumn colors is greatly influenced by the weather. Low temperatures destroy chlorophyll, and if they stay above freezing, promote the formation of anthocyanins. Bright sunshine also destroys chlorophyll and enhances anthocyanin production. Dry weather, by increasing sugar concentration in sap, also increases the amount of anthocyanin. So the brightest autumn colors are produced when dry, sunny days are followed by cool, dry nights.

SO SIMPLY...THE COLOR CHANGE IN THE BACK COUNTRY IS NOW REACTING TO THE OCCASIONAL COOLER AND DRIER THAN NORMAL WEATHER OVER THE PAST WEEKS IN THE HIGH COUNTRY...THE COLOR CHANGE IS NOT A FORECASTER OF THE FUTURE...BUT A REMINDER OF THE PAST. "

Michael, good stuff. Here in the Northeast, best autumn color also seems to be related to rainfall over the summer - if the summer was dry, leaves simply turn from green to brown and fall off the trees. We've had plenty of rain so far this summer, so hopefully we'll have a colorful autumn.

This is a basic concept taught in the early years of HS, but apparently forgotten all too often.

I've found that the primary determinant of decent fall colors is frost at night, in states east of the Mississippi. While rainfall may determine if the quality is fair to excellent, lack of cold nights means no decent color. The terrible fall color in Vermont last year was due to lack of frost. I was in Stowe last fall, and tender annuals were still in bloom. So tracking temps in an area gives a good indication if trees will turn, or the leaves just turn brown and fall off.
State fall color reporting is highly variable. Vermont is completely detached from reality: the color is always good. New York State is highly reliable, as the report is done by earnest forest service employees, not the travel industry. Most states are in between. Wisconsin, for example, has a centralized reporting service with the information fed by each town. Some towns are more accurate/honest than others. In all states the forecast of "number of weeks to peak" is just a guess and usually inaccurate.
Calling Inns and asking how the color is looking is almost always reliable. They know they may see the caller face to face.
The best way to photograph color in the Appalachians is to have the flexibility to move north and south. It's always good somewhere. If you like to drive, you're good to go.
I would like to hear how others do their planning.