In 2009, a group of mostly white students were questioned about their political leanings and then shown three pictures of Barack Obama. The president's skin had been digitally lightened in one photo, darkened in another, and left completely unaltered in the last. The students were asked which image showed his "true essence." The liberal students were twice as likely to pick out the lighter picture, presumably because they believed "his true essence" meant "which picture looks like his soul is trying to leave his body." The more conservative students picked the darker one, unless they had actually voted for Obama, in which case they were also more likely to pick the lighter picture. Just in case the students were being influenced by the fact that Obama is a real person, the researchers ran another study with an image of a "racially ambiguous" fake politician and got the same results. This was presumably a photograph of Dwayne "The Rock" Johnson in a suit.
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Seen here with his "racially ambiguous" 2016 running mate.
The research indicates that when you like or agree with someone, you tend to associate that person with having a lighter skin tone. When you disagree with them, you perceive them as being darker on the outside, as if all their internal negative qualities were somehow dirtying their outward appearance to warn you about their nefarious true nature. You might recognize that statement as the worst thing you have ever read.