I don't know what softer tan looks like, but I'm assuming it's a tan/beige neutral. Regardless, carrera marble is also totally a neutral and any paint color will go with it. Good luck!! And re: your flooring, you could do carrera marble tiles on the floor, too, to tie everything together, or you could go all retro and use an old-fashioned white hex tile, or a basketweave. Again, carrera goes with everything so I wouldn't worry about it too much. Anything gray-ish or white-ish will do for the floor, and will go with your white beadboard and (I assume) your white tub, toilet, and sink. And once the floor and the countertop go together, it doesn't matter what color the walls are painted.

Yes, you have to try a pretty large swatch on your own walls to make sure a color will work. I had spent a lot of time picking the colors for my house in the northeast. When I moved to CA I thought I could just use the same colors. Wrong! The colors I had loved in the old house did not work in the new house. I had to repaint the whole downstairs after that mistake!

I had my den painted Kilm Beige and I was very unhappy with it.  In my house, it leaned peach and was dark at night.  My husband went to work and I repainted with SW White Duck and I LOVE it.

PPG's Delicate White. I use Swatch Right paint-peel-and-stick decals for trim and moldings because they're a thin film and will conform to the details.