With the many changes in chemistry going on because of mutations the color scheme of the natural world has had significant changes since the Cataclysm. All colors are possible and there are many individual plants that have leaves of different colors or many colors (i.e. different branches having different colored leaves vs leaves that have two or more colors). The colors found in any particular location are random to a point. Those that are prefered food will be in less abundance and color is an important cue for many animals in what is and isn't edible. As for white plants, they are predatory or use an alternate source of energy such as sound or heat.

 

Then there are those plants that change color quickly enough for humans to notice. This may result from a hazard such as radiation, parasite infestation, or coming weather. It may also be the way the plants communicate with each other or with the animals around them. The easy way to find if this is true is observe the plants and see if they have eyes. Slower changes may occur because of diet (the minerals and chemicals they absorb) or climate. Plants that change color because of the turn of the seasons may have different mutations as a result.

 

The most dangerous plant colors are those that edge on the unnatural. They can lure, dazzle, confuse, charm, intoxicate, cause unconsciousness, or even physical harm to both biological and technological organisms (i.e. androids and robots). Plants in one location generally have the same effect as they are all drawing on whatever superscience pollution or technology that allows them to produce the effect. If something changes in the environment and the source is altered or removed, then the plants will have new powers or be bereft.

 

And finally there are those plant mutations that have specific colors associated with them. Unless the mutant has a modifier (Wisdom from the Wastelands #20) or another mutation that allows for a change in appearance, some of their innate powers will be obvious to anyone with eyes and can see color. If the plants themselves have eyes, it is possible for plants with hostile colors and patterns can affect each other. Plant versus plant combat can get so dizzying that animal either flee or go comastose until the battle is over.

 

Oh, and obviously all of this applies to the plant's bark, roots and other tissues. What may seem like a normal tree may have lumber that causes problems when it is debarked or simply cut down. Or the roots of a plant affect those who burrow and have a source of light. In that case some locations underground may only be safe in the dark...