Marble is chosen for the veining, and veining cannot be specified. Each of these basins is cut from a single block, so the gray runs where the quarry put it and the piece that reaches you is the only one exactly like it.
Carrara gives the softer, more even gray most people picture. The other stones here run darker or warmer and suit a room that already has a strong floor. All of them are honed rather than polished, which reads quieter under bathroom lighting and does not show water spotting the way a mirror polish does.
Marble is porous. Ours arrive sealed and stay well with nothing more than a pH neutral cleaner, but they should not meet limescale removers or anything acidic. The cleaning guide on each product page says exactly what to use.