(CNN) -- What gives M&Ms their bright colors? That depends on which country you're in.
Mars Inc. primarily uses artificial food coloring for the candy in the United States, but M&Ms derive their candy coloring from natural sources in Europe.
Now a Change.org petition begun by Renee Shutters and the Center for Science in the Public Interest is calling on Mars to stop using artificial dyes in its American M&Ms as well. As of Tuesday morning, the petition had more than 142,000 supporters.
Shutters says her son Trenton showed noticeable improvements in mood and attention span after she removed artificial coloring from his diet a few years ago. M&Ms were his favorite candy.
"I just could not believe that something so small could make that big of a difference," Shutters says.
European lawmakers moved to require warning labels on foods containing certain artificial colorings after a 2007 study found a slight increase in hyperactivity among children consuming a mixture of the dyes and a preservative.
The required label reads: "May have an adverse effect on activity and attention in children."
The move came despite the European Food Safety Authority's conclusion that the UK study "provides limited evidence" and "cannot be used as a basis for altering the (accepted daily intake) of the respective food (colors)."
Instead of adding the warning, most manufacturers voluntarily switched to dyes derived from natural sources, such as beets or annatto for red, carrots for orange and saffron for yellow.
In the United States, the Food and Drug Administration has declined to implement tougher regulations but acknowledged that "certain susceptible children with Attention Deficit/Hyperactivity Disorder and other problem behaviors" may have their condition "exacerbated by exposure to a number of substances in food, including, but not limited to, synthetic color additives."
The effects on behavior "appear to be due to a unique intolerance to these substances and not to any inherent neurotoxic properties," the FDA said in 2011.
Michael Jacobson, executive director of the Center for Science in the Public Interest, says the FDA and big business need to take action.
"The Food and Drug Administration should protect the public's health by banning food dyes," Jacobson says. "Companies of course could remove dyes voluntarily, switching to safer natural colorings, and a few big companies are beginning to do it."
In November, Kraft announced it would be removing artificial dyes from some varieties of its Macaroni & Cheese.
"We have absolute confidence in the safety of all the ingredients we use," Mars said in a statement. "(We) are constantly evaluating and updating ingredients based on consumer preference, new technology, scientific information and availability of raw materials."