I voted white : a person might need to see a light/dark contrast between shower bench and floor. Which would be easier to keep clean ? Does bathroom vanity have to match ? What accent "pop" of color will you use ? It will be lovely, when finished.

My white vote because black will show all dust, soap residue, water spots, etc. Just keeping up with slate bathroom floor is a lot-- unless you are the sort of person who wipes up everything immediately -- and anyone you live with has the same level of tidiness .

White to lighten up the space. The dark floor is really nice and grounds the room but a black counter top is just too much darkness

Thanks all for the suggestions! This is so helpful!! I’m siding with the white as well. Glad to get affirmation.