Kraft's Guacamole Dip in the dairy case looks tempting -- until you learn that its vibrant green color doesn't come from avocados (there are almost none in it) but from synthetic food dyes Yellow 5, Yellow 6 and Blue 1.

Think Aunt Jemima Blueberry Waffles have real blueberries? The blue color actually comes from Red 40 and Blue 2.

And don't even think that the colors of Kellogg's Froot Loops, other sugary cereals and General Mills' Fruit Roll-Ups have anything to do with real fruit. You can thank synthetic dyes for brightening up those foods, too.

While the use of food dyes has been a concern for years, the nonprofit watchdog group Center for Science in the Public Interest last week made a plea to the Food and Drug Administration to ban the chemical in American foods.

These dyes have been suspected of causing hyperactivity in children since the 1970s, when Dr. Ben Feingold, a San Francisco allergist, noted that his patients improved when they avoided the ingredient.

Controlled studies conducted over the next 30 years in the United States, Europe and Australia confirmed that the synthetic dyes worsened the behavior of some children, according to the Washington-based consumer group.

The FDA has disputed these results. "Well-controlled studies since then have produced no evidence that food color additives cause hyperactivity or learning disabilities in children," the FDA says on its Web site.

Of particular urgency is the fact that Americans' exposure to these dyes has risen sharply over the years. In 1955, the amount of food dye certified for use by the FDA was 12 milligrams per capita per day. Today, that certified use has leapt to 59 milligrams per capita per day -- nearly five times as much.

The center has filed a petition asking the FDA to require a warning label on foods with artificial dyes until it acts on the organization's request to ban the dyes altogether.

Across the Atlantic, the British government has aimed its attack against the dyes on food manufacturers with growing success. That's why when you order a sundae with strawberry sauce from a McDonald's in England, the sauce is made of strawberries. In the United States, it's Red 40.

Late last year, Mars banished artificial colors from its well-known Starburst and Skittles candies sold in the U.K. Northfield, Ill.-based Kraft did the same in early 2007 with its British version of Lunchables.

"This is about listening to consumers," said Kraft spokesman Michael Mitchell.

Thus far, however, U.S. consumers haven't spoken up enough to cause big manufacturers to drop the dyes, which are ubiquitous in American foods.

In the United States, you can avoid these dyes if you shop at Trader Joe's, Whole Foods or other natural health stores because they don't carry products with these controversial chemicals.

But most commercial products at regular chain groceries and mass merchandisers do, even foods that aren't particularly colorful to begin with. That would include Betty Crocker's Au Gratin 100 percent Real Potatoes, which turns out isn't all real potatoes.

You can thank Yellow 5 and Yellow 6 for the colors, which come from coal tar.

Yum.