Look at the number of nuts who have used the word treason to apply to President Obama. At least half of that caused by the president not being snow white in color.
If you really believe that even a sizable minority of the negative feelings about Obama are racially motivated, then you're just mistaken. Sure, the racists are out there, but they are really just background noise.
I live in the south, and I personally know dozens of people who traditionally vote Republican who voted for Obama in 2008 specifically because he is black. My father was one of these people, and he said to me after the election that "it's just time for a black president." If anything, Obama received a huge boost from the fact that he was the first credible black candidate for president, and it helped that his competition was lackluster at best.
No, the people calling Obama treasonous or calling for impeachment are much more likely to be basing this on Obama's actions while in office. By and large, it's not the color of Obama's skin that they're judging, but rather the content of his character.