Question about discrimination lawsuit against Denny's

I wasn’t sure if this was a GQ or GD, but I thought I’d start it here. Mods, please move if you need to.

Several years ago, Denny’s was sued for discriminating against blacks. (I’m glad Denny’s lost, BTW. That whole situation was sick.)

My question is, it is legal to discrimate against customers on the basis of race? I wonder because Denny’s was sued in civil court, and I didn’t hear that anyone was arrested over this matter, which would make it criminal.

IANAL, so I may be misunderstanding the situation. I know you can’t discriminate when you’re hiring someone or selling or renting a home. Can you discriminate against a customer, and the only recourse they have is civil, not criminal? Are there laws in place to protect customers against discrimination?

There’s a difference between a criminal illegality and a civil illegality. For example, a company I worked for (for a very short while) decided they weren’t going to provide me my paycheck because they were upset I quit on them when they started to jerk me around. Well, it’s illegal to withhold my paycheck from me, especially after I’ve already earned the money; however, it’s not a criminal act–it’s a civil offense for which my remedy was to threaten to sue.

Here’s an example from Minnesota Civil Rights law. http://www.humanrights.state.mn.us/site/docs/rights_yours.html

The US Civil Rights Act has similar provisions. A similar page didn’t show up in quick google search but it’s surely out there.