These diets are based on the idea that the more vibrant the color of food the better it is for you. In a nutshell it's another way of getting you to eat more vegetables.
Vegetables. Bright colored ones. Vegetables that are vibrant in colors typically harbor potent phytochemicals and numerous antioxidants. Certain colors supposedly have specific phytochemical effects.
Good colors include:
Red to fight arthritic pain.
Good red choices include apples, beets, cherries, cranberries, raspberries, red onions, tomatoes or watermelons.
Green to preserve eyesight.
Good green choices include artichokes, asparagus, avocado, broccoli, brussel sprouts, celery, cucumbers, green beans and green peas.
Bad colors include:
White. These foods are generally low in nutritional value.
White foods include white flour, white rice or sugar.
Lighter Greens which have "empty" calories.
Iceberg lettuce found on most burgers at fast food places is a lighter green. It may be more nutritious to eat the napkin instead.
How it Works
Phytochemicals, those hundreds of different compounds that plants produce to protect themselves can offer protection for humans. Since phytochemicals are also responsible for the pigments (colors) of plants you can increase your health benefits by eating specific colors.
These diets encourage you to eat many more vegetables and long term studies have shown that people who eat more produce have lower rates of chronic diseases.
Pros and Cons
Americans tend to eat only 3.4 servings a day of vegetables (according to the National Cancer Institute) instead of the USDA's recommendation of "5 a Day."
These books may encourage more people to eat better by offering over-weight people another way to view food and make better choices.
The bad part is many studies about certain fruits and vegetables and their "healthful" properties are preliminary. If you are eating foods to fight off specific diseases you may be risking your health because long-term studies haven't been carried out or completed yet. While eating vegetables to be healthy is a good idea, eating them to protect you from cancer or other specific health risks is a gamble.
The Bottom Line
Choosing what you eat because of its color is definitely a gimmick. But ultimately any program that encourages people to eat more vegetables is a good thing. Just don't fall for the claims these diets make of curing or preventing any specific diseases.
As with any diet what these books suggest should NEVER be attempted without the supervision of a Medical Doctor or licensed Nutritionist.
General Reference Links
American Heart Association
Center for Science in the Public Interest
Centers for Disease Control and Prevention
National Institutes of Health
United States Department of Agriculture