Please cite me a law that would make a advertisement that showed a race in a poor light.
The most important federal government controls over advertising are exercised by the Federal Trade Commission. In addition, broadcasters self-regulate and are given the right to refuse advertising messages (with an exception for certain political ads). And states can regulate commercial messages.
The US Supreme Court laid out a four-part test on regulating commercial advertising: one, whether the expression is protected by the First Amendment (must concern a legal activity and not be misleading or fraudulent), and two, if government interest in restricting the commercial speech is substantial, and three, if regulation directly advances this government interest, and four, whether the regulation is more extensive than necessary to serve that interest.
The content of an advertisement is important. You saw government restrictions on tobacco advertising, for an example, and some states regulate ads for alcohol. Content can be censored.