Simply Designed Expressions and then simply placed them on bathroom sized 4x4 tiles from Lowe's and Home Depot. The two different stores carry different color tiles, so if you love colored tiles, check both places.
I made one for my sister and she chose to make her with all black vinyl on sand colored tiles and I went a little crazy on colors for mine. It is one of my favorite decorations in my house and one of the first things I change when I am decorating for a new season. The patterns* are included, so you can make your own.
*This pattern is intended for personal use only.