It's autumn. Somebody tell the trees. From a report: Ordinarily, two signals alert deciduous trees that it's time to relinquish the green hues of summer in favor of autumn's yellows, oranges and reds. First, the days begin to grow shorter. Second, the temperature begins to drop. But this year, unseasonably warm weather across most of the U.S. has tricked trees into delaying the onset of fall's color extravaganza. Temperatures in the eastern half of the country have been as much as 15 degrees above normal since mid-September, and the warmth is expected to persist through the end of October. The unfortunate result for leaf peepers is a lackluster fall. Two kinds of pigments produce the season's liveliest foliage. Carotenoid, responsible for yellows and oranges, is always present in leaves but is usually masked by chlorophyll. The initial trigger for its appearance is shorter days. Anthocyanin, responsible for reds and deep purples, is different. Not all deciduous trees have this pigment, and those that do manufacture it from scratch in the fall. The primary trigger for its appearance is lower temperatures. Without that cooling cue, the colors of maple and other species that generally ignite New England with brilliant reds this time of year are likely to fizzle.