For the record, your civil rights claim is weak at best.
It is not illegal to be a racist. It is only illegal to make employment decisions based on race, or to create a hostile work environment on the basis of an employee's race. Your boyfriend was not fired, demoted, or even harassed on account of his race; he overheard one conversation in which racist comments were made (which is NOT sufficient to create a hostile work environment) and at most it was insinuated that the client did not want him there. If you have provided us with all the facts, no one acted on the clients' views, even assuming that the client actually said such a thing.
Terming him for inquiring about his hours may or may not have been illegal depending on the specific details; however, Florida has very weak wage and hour laws. If I recall Florida statutes correctly, unless he inquired IN WRITING AND gave the employer sufficient time to correct the situation, then an internal complaint is not protected under state whistleblower laws. His case would have been FAR stronger had he made his complaint to the state DOL; it's definitely illegal to fire someone for filing a complaint with a regulatory agency - it's not necessarily illegal to fire someone for complaining internally. And, of course, this is a completely separate issue from the civil rights claim - on the basis of what you have posted there is no overlap whatsoever.
Just something to keep in mind during the mediation.