I think that red colors in deciduous trees are often caused by the sugars left over after the leaves dry up and loose their chlorophyll.
I think you're right; I seem to recall hearing that the chlorophyll death in the leaves exposed some other pigment or something that makes the leaves look red.
What if the trees do not photosynthesize, they use their roots to drain small beet-like plants that grow under the trees branches. The leaves keep animals from eating the beet-things (thats why the tree keeps them). Most of the animals on this age are hurt by the color red (it has something to do with their eyes). The other colors may have something to do with the chemical make up of the soil or some other reason.
Hmm, interesting idea!

There's another way to explain the red tree colors, but I like how you think in terms of species interdependency and ecosystems. If you have any other ideas about what the jungle plant species might be doing, I'd be interested in hearing them.

Hmmm? So, if its red, you are not going with photosynthesis.
Well, the basic cause of plant greenness is that chlorophyll, a photosynthetic pigment, reflects green light that enters your eyes. If another photosynthetic pigment (something like retinal, perhaps) were to reflect red light instead of green, then you would have red plants because the reflected red light would enter your eyes and you would perceive the plants as being red. Actually, there are lots of plants here on Earth that don't use chlorophyll as their photosynthetic pigment or don't reflect mainly green light, including lichens (yay!), various species of algae and bacteria, and, even "normal" vascular plants. It is even hypothesized that the first photosynthesizers might have looked purple due to a photosynthetic pigment they may have used! So, green chlorophyll isn't a requirement for photosynthesis; you just need a photosynthetic pigment (which isn't restricted to green) with which to absorb light.
I read these articles about the topic of plant colors and photosynthetic pigments; pretty interesting stuff.
http://www.sciam.com/article.cfm?SID=mail&articleID=E2CEE13F-E7F2-99DF-34E77CE94449C048&chanID=sa003http://theforcethat.blogspot.com/2007/04/why-are-plants-green.htmlhttp://www.livescience.com/environment/070410_purple_earth.html