The racism in the Trayvon case is here:

The justification [of self-defense]… is not available to a person who… initially provokes the use of force against himself or herself, unless… Such force is so great that the person reasonably believes that he or she is in imminent danger of death or great bodily harm….

There’s the racism. Right there.

It all hinges on that “reasonable belief”. In the culture of racial anxiety and safety paranoia that dominates certain swathes of the USA, it is much easier for a jury to accept that a white man reasonably believes he is in such danger from a black man, than the reverse.

(Note that the accused doesn’t need to be a racist for this to have an effect. Nor does the judge, nor the prosecution or defence, nor the jury.)
(Yes, Zimmerman wasn’t white. Still counts.)
(Yes, the legislation says that the basis of the belief must be the degree of force. Still counts. A punch from a black man is straight-up more terrifying than a punch from a white man.)
(The blockquote above is my selective quoting from the relevant Florida legislation, as excerpted by Ta-Nehisi Coates – read his post too.)