Once your bathroom or kitchen tile job is done, and the grout has all been set, you'll probably have some leftover grout left by the contractors. Another thing you should have is a small supply of leftover tiles - your contractor should over purchase tile by about 10% They do this because lead time for ordering tile can be a hefty, so over-ordering by 10% is a fairly standard practice to avoid gruesome delays.
With all these leftovers, you need to figure out what to do with all this stuff, if, like most, you are short on storage space, you need to make do. Don't get me wrong, tile can be stored in crawl spaces, or basements if possible, but the point of this picture is to illustrate good use of excess materials.
In this picture, we have a spare 6 inch tile, with both colors of grout smeared on the business side of the spare tile. Using this one sample of tile, you can match future grout needs or even match paint. This sample can be taken to any paint store for matching when any touch up is ever needed, or a matching paint