You can contact the Department of Labor (http://www.labor.ca.gov/), but I seriously doubt what they did has any legal consequence.
I don't know about CA specifically, but Departments of Labor usually LOVE aggressively defending employees' rights. Something I don't see much on HN, but I saw a LOT when I worked in HR.
> Departments of Labor usually LOVE aggressively defending employees' rights
In my experience this is only true if it is easily proven that you were fired because of blatant racism or sexism. If it isn't either of those two reasons or it is harder to prove, nothing will happen.
To the OP, yes it seems perfectly legal, you can be fired at any time for any reason that isn't one of a handful of protected reasons (sex, religion, race etc.). You can be fired for wearing blue that day if they so feel like it. It's just not usually so petty because it can be a little bit of a cost replacing a person.
I don't know about CA specifically, but Departments of Labor usually LOVE aggressively defending employees' rights. Something I don't see much on HN, but I saw a LOT when I worked in HR.