(Newser) – The GOP may have intentionally darkened President Obama's skin in ads during the 2008 presidential campaign in order to capitalize on racial biases, the Washington Post reports. According to a study published Dec. 17 in Public Opinion Quarterly, 86% of attack ads attempting to link Obama to criminal activity made his skin look much darker than it naturally appears. "There is strong evidence linking skin complexion to negative stereotypes and adverse real-world outcomes," the study's authors write. Past studies have shown racial bias increases as skin tones get darker, the Post reports.

Researchers looked at 126 ads released during the 2008 presidential campaign, the Post reports. They found Obama's skin got darker in John McCain's attack ads while McCain's own skin lightened as the election got closer. Researchers can't say whether the manipulation was intentional, but the Post states: "The finding reinforces charges that some Republican politicians seek to win votes by implying support for racist views and ethnic hierarchies, without voicing those prejudices explicitly." Researchers manipulated their own photos of Obama and found those who looked at a picture of a darker Obama were more likely to give a racial stereotype as an answer to a fill-in-the-blank game. "A subtle darkness manipulation is sufficient to activate the most negative stereotypes about Blacks—even when the candidate is a famous counter-stereotypical exemplar," they write. (Read more Barack Obama stories.)

