Andrew Gabriel wrote:

Get plenty of spare tiles. Some places will happily do a sale or
return basis, but don't assume you will be able to go back later
and buy any more matching tiles. Both types I used seemed to cease
to exist within a month, but fortunately I have plenty left over.

And in any case, you should always buy tiles with the same batch number
as the colour shade may vary a bit across batches. (And always check
every box you buy, as there's no guarantee that Andrew hasn't been in
yesterday returning a box from an old batch number, bought a few months
ago) :-)

David