In some circumstances, it's not harmful to assume the person wearing a suit is the CEO, though you might not always be right. The person in the suit might also be head of sales, while baggy clothes is CEO. Generally, it's better not to assume at all unless you're forced to. Just ask.
But inferring that someone isn't the CEO because they're black? I'm sorry, but that's racism pure and simple. Stereotyping is one form of racism (not the only one). You have no reason to make the inference, and it's highly insulting if you make a mistake. And to assume that feelings wouldn't be hurt is... tremendously naive and blind to the reality of racism.
If I were to meet/know/whatever 100 CEOs and 99% of them were not black and for example wore an expensive suit in a specific setting/environment, then is it racist to assume (based on my past experiences) that a particular black person wearing an expensive suit in this particular setting/environment is not the CEO? I honestly fail to see how making assumptions based on personal experiences and whatnot is racist. This is not equivalent to claiming that someone who is black cannot be the CEO, there is the possibility, most definitely. Denying this possibility based on race or skin color is what I would rather have a problem with.
What a person feels is subjective and has nothing to do with what the other person intended to do. As you can't be in other people's head (except if you have that pretension ?) the only thing that matters is what your intention were.