If you have stainless appliances, then a stainless prep sink is not a disparate element. I like stainless prep sinks and think it would look great next to the carrera.

Silver always looks good with Carrara, but I really dislike ss sinks. Have you considered silgranit? Blanco's metallic gray sink is a beauty. From a distance I thought it was a nicer ss sink but without the ss water marks. It sparkles just a bit, but isn't gaudy. It looks great with Carrara, especially if it has any charcoal veining. In fact, I'm using the metallic gray for my cleanup sink with honed Carrara. If I put the Carrara on my island too, I'll do the metallic gray for my prep sink also.

I think if you choose to have them not match, one of them should reflect a dramatic upgrade. Like a polished nickel drainboard main sink, or a super-shallow veg sink, or whatever. That way you see intentionality at the root as opposed to a dropped ball.
In your case, I'd suggest a polished stainless zero-radius prep sink. That's dramatic.
Casey

We at MR Direct have an undermount white kitchen prep sink that matches our farmhouse apron sink. It may of interest if you are looking for matching elements.

Here is a link that might be useful: White Porcelain Prep Sink

MR Direct Spam, huh? Given the current thread about trojans hiding in images, I'd skip it and stick to searching known sources. I've never liked Spam anyway. ;-)

Wasn't sure what you meant by match when I opened this -- mine are both stainless but one is zero radius and the other is not. Stainless does go well with marble and I don't see it as a disparate element either. It's just another use of the stainless you will already have.