After your tiling has been done, keep some spares to replace tiles which may get cracked e.g. when the repair man comes to mend the washing machine!

The average shelf life of a ceramic tile is about 5 years after which it is usually discontinued so it is fruitless to try and match existing tiles. When you purchase tiles, keep a record of the reference number(s) and the few with are inevitably left over when the job is complete.