Ask Mr. Answer Person: "Why do leaf colors vary from year to year?"

The Porter House, framed by fall colors

Rich asks Mr. Answer Person: "Why does the fall leaf color on trees vary from year to year?"
 
It's the type of weather that arrives in early fall that largely determines the intensity and duration of fall leaf colors. 

The tree species that are capable of producing good fall color like it when days in early fall are sunny and mild and nights are cool but remain above freezing.

The trees don't like it as much when there are long periods of cloudy, rainy weather in early fall or a hard freeze in early fall.  In cases like that, the fall color displays are more muted.