I can't help you with the backsplash, but I have a question. Where did you find a designer who would work with you if you didn't buy the cabinets from her? Of does Ikea offer designers?

My "designer" is the contractor's wife. She figured out how to fit things in my tiny kitchen. I want anything except white ceramic subways.

Maybe the color is off on my screen. Are your cabinets CREAM or white? I just don't understand why she would say marble wouldn't look good but a WHITE subway would. I think white subway would be about the most boring choice you could go with for that space. It isn't like AB granite is a show stopper you need to tame. I actually think marble would look really pretty from the pic I am seeing. And, keep in mind a motto here-a designer doesn't have to cook in your kitchen-YOU do! So get what YOU want. WIth AB and white cabinets, you can really do just about anything-mosaic, subway, color splashes, stones.....

You could go a smaller "subway" and with color variation. Yes, white subway is the classic and many have it (mine are more cream) but you certainly can deviate.
I get what your KD is saying about the marble, but I wouldn't write it off just yet. Maybe she is thinking it will not blend with the white color of your cabinets. There are many different variations out there, so maybe you can find one that will suit your color cabinets.
With two plain elements, you can have the backsplash be the star.

I think marble would be beautiful - just make sure to seal it every year. If you don't want white subways, don't do it! You need to be happy. There are colored subways that could work, or glass subways. And if you don't like the rectangular shape...what about squares on a diagonal? Or white Arabesque? Or just painted wall as a backsplash until you find something that speaks to you? I swore I didn't want white boring subway tile...but at the 11th hour, I found a beautiful mosaic that I fell in love with...put it behind the range with undulated white subways for the rest of the backsplash. Just keep looking at different tile stores until you are happy :-)

Actually, the cabinets are more of a creamy white. The marble I was looking at had gray veining, which would have clashed. A pure white marble or a marble with more cream veining might go better. The designer was also saying that it could get expensive if we bring it all the way up to the ceiling, but I would be happy with bring it up to the bottom of the cabinets.

This has been very helpful. Thank you everyone! I would love more suggestions.

If it is a creamy white, I'd think white subways would clash as well. I'd just keep looking at inspiration pics on houzz.com and such and find something YOU really love.

if it's a small kitchen -that's a factor. What is the floor? I have 2 theories on REALLY small kitchens-if you can't lick em,join em-means go cottagey/quaint/eclectic/let it stand out and be "special"-there won't be that much of it. Or-the whole space gets streamlined/reflective/monochromatic/etc. You can do color square ceramics/you can put inserts with tile on the diagonal/it just depends on how you want to feel when you are in there. Is the "cape" feel to your home pretty authentic? I'd want something special I guess-just go and really look at tile for it's merits-what is pretty or interesting to you? Tile has so many variations-porcelin is beautiful/mosaics are nice-but not all of them are appealing/textured or plain/use of inserts could really beautify it and work with the hardware to make it eye catching....

I agree that a carrara (grayish/cool) would not look great with creamy/warm cabinets. I too wanted carrara but shied away because my cabinets are cream. I was considering calacatta marble subway tile, which has more gold tones.

Ultimately, I decided against the marble subway tile and went with a staggered set white glass staggered set tile. My kitchen is similar to the picture attached (similar cabinets and the same backsplash and kashmir white granite).

I ordered the B/S online and, other than a small sample in another pattern, never saw it before it was installed. We were away on vacation when it was installed. The problem is that since it is a glass, this tile is transparent. My contractor had painted the entire kitchen right after sheetrocking in BM coventry gray (which is a blue gray shade.) So, the B/S shows some of the underlying paint and it is a slightly lighter shade than the walls. I was livid at first but I actually really like it now. I'll post pictures soon....

Good luck with your decision!!

Here is a link that might be useful: vetro stagger set tile.

Look at Star7's last picture of her newly installed backsplash.

The kitchen is really small. The pictures are of what it will look like. We have a walnut floor. The house is in fact a 1930's Cape.
I really like Star7's glass tile backsplash. Maybe some sort of glass tile mosaic.