To what may we attribute a poor color year?

It is October 26, long past our usual peak for fall color at this elevation, and yet, some of the leaves are still green.  Others have a yellow-ish tinge to them, but seem more dry and dead than colorful.  Still other trees changed color some time ago and are now bare.

When I lived in Iowa, about one year in four would be a (comparitively) poor color year.  (Three out of four years were spectacular.  The other year was merely splendid.)  Usually, this was because of rains which washed the color out of the leaves.  One year, it was because there wasn't enough September sun.  (Fall color is aided by sunny days and cool nights.)

Here, we had the sun, and cool nights, but almost no late summer precipitation.  What it looks like is that the trees are too dry to muster up the energy for really good color.