Pop quiz: Which of the candy bars below is healthier?

You probably chose the top one, even though the two bars—and their accompanying labels—display exactly the same information. The key difference, as one new study in the journal Health Communicationsˆ finds, is simply the color of the accompanying labels.

Labels like the ones above might look familiar. Back in 2009, candy company Mars introduced "Guideline Daily Amounts" labels, meant to help consumers understand a specific product in terms of overall recommended caloric intake. A packet of M&Ms, for example, would account for 12 percent of recommended caloric intake for a day.

"Mars reportedly settled on this particular label design after market research revealed it was 'the clear favorite among consumers,'" Cornell University's Jonathan Schudlt writes. But he started wondering whether the label and, in particular, its choice of a green background might serve a purpose for the manufacturer. It may make the food seem a bit healthier, with a green light to go ahead and eat.

Schudlt came up with two other labels that replaced the green color with a red one. He then ask study participants, viewing the two different colors, how healthy they thought this candy bar was compared to other offerings. On a scale of 1 to 9, the candy bars with a green label ranked as healthier than those with a red label, despite all other data (the picture, the nutrition information) being held constant.

"A candy bar was perceived as healthier when it bore a green front-of-package calorie label than when it bore a red calorie label, despite the labels displaying the same calorie information," he writes. Although the choice of green labels over white or any other color may appear to be a purely aesthetic one, the present results suggest that green labels carry a health halo that encourages consumers to see a relatively poor nutrition food (a candy bar) as healthier than they otherwise would."

Something to think about next time you see a green label in the grocery store.