Here is my Mommy's cute explanation (it says pretty much the same things as the website Freckles linked to):

Hi Kate. I'm sure that there are some websites that could give you more detailed information, but just to give you some of what I know.

First: there are two groups of pigments involved: one are the yellows (xanthophylls) and the orange to red-orange(carotenoids - yes the same that gives carrots their color.) These two groups of pigments occur naturally in leaves of plants and are sometimes called accessory pigments in the photosynthetic process, because they capture some of the sunlight energy wavelengths that chlorophyll cannot, and "pass" that light energy on to the photosynthetic process.

When the leaf dies with the onset of cold weather, the chlorophyll pigment breaks down and disappears. However, the yellows and orange pigments last longer and give many leaves that color. Eventually they break down and the leaves turn brown.

The second group gives the red to red-blue colors in the leaves that are due to the pigments called anthocyanins. They also give flowers red to purple colors, as well as red cabbage and beets. When growing conditions and weather are just right (has to do with temperature and rainfall), these colors will develop more intensely and as I understand are related to sugars the leaves make and somehow (I don't know why) convert into these bright red-blue pigments.

As you may have noticed, some very colorful leaves have all these colors highly developed, others seen to specialize in one or two colors only.

As to certain species of trees having certain color patterns, that is certainly the case. I used to know which certain species of oaks and maples had which types of colors, but can't remember all that now. If an oak tree turns red this year, I think it is pretty much genetically determined that it will every year. However, the climatic conditions I mentioned above have a big impact on the intensity. So some years, fall coloration will be very intense for all trees, and other years, not so much of a display.

Also, in recent years, hybridists have developed cultivars of maples, and maybe for other trees, which have especially enhanced fall coloration!

What a smart and eloquent lady! I'm so proud to be her daughter!