We had some ancient mosaic tiles that were rotting off the wall. I had no replacements BUT I did have a tile placemat I had bought at the thrift store for $1. I didn't have enough tiles from the place mat, so I got out my polymer clay and made tiles to match.
Here is a picture of the shower ledge I retiled with my $1 place mat tiles and the matching polymer clay tiles. Even up close people can't tell which ones are the polymer clay. And the best part? This was done 6 years ago and the tiles and the grout have not even been touched up! Even through all the shower use and scrubbings the tile looks as good as new!