Floor & Decor has a nice blue penny tile that should work on a shower floor -- color is a bit variegated, which would help with the water illusion...It's porcelain, and the pennies are basically penny size, so there's plenty of room for grout...

I’d jettison the marble in the rest of the bath. Go with something else in porcelain that offers the same thing in a 2x2 for the shower. I don’t care for high maintenance marble in a bath period. Unless you’re not the one caring for it and you throw away all conventional cleaning products and the maid doesn’t bring in anything from outside.

I've been installing Ditra since "92" when it was in a straight line. Not the waffle pattern of current and Kerdi since it came out. So I also have some experience. Now I use other systems. Times change and products change. There is drywall compound in the photo. That's a big concern as TFW pointed out. Yes Schluter and others approve their systems over drywall. A product that has not been allowed in a wet area since 2006. Any moisture/condensation in the wall cavity, dripping valve, cracked O ring, a leaking pipe, etc. will deteriorate the drywall from behind the waterproofing membrane. No warranty there. Yes these systems that state this is acceptable can bond to the drywall. I could put up cardboard and bond to it also but it doesn't make it correct. Point to consider. USG makes drywall and a waterproofing membrane yet will not approve this method. Using a CBU eliminates this risk. Just raising a point to consider.

Thanks for all input so far! I will eliminate the travertine from the mix. It was a suggestion from the tile guy but I had doubts on it from the start. I will also be painting the oak trim white. Regarding the counter vanity - not in budget to change it. Ideally I’d swap out the whole vanity - totally get that it is warmer. I could think about painting the vanity but that would be a last resort. So there were a number of replies saying the marble doesn’t work. Is it the colors or pattern? The pattern is very minimal with some beiges and grey whereas most others I’ve looked at are more grey or gold with more color overall which I thought was too much. This is a ceramic calacutta bianco but there is a calacutta creme too which I will get a sample of. There wasn’t much feedback on the floor - it is slightly more cool than the counter but has some of the same tones as the flecks in the counter. Additional pics of counter with tiles ... open to suggestions on other tiles to consider. I just don’t want to go too yellow.