It would definitely be better to use the cream to match the tile, as the black grout will compete with your shower pattern. Black would also point out any irregular pattern to the tile, such as cuts around commodes, or vanities. The cream will allow the eye to nicely flow around the entire room, without a cut-up look,and giving it a richer look overall. Most bathrooms are not large enough to handle both the harlequin pattern and such a strong pattern that the black grout would create.
