Use a Hydroment grout color chart by looking at the various colors and selecting one based on your tile color and individual preferences. Bostik, Hydroment's manufacturer, produces grout products in a wide variety of colors, from neutral tones like beige and gray to much more vibrant oranges, reds and greens.
Before purchasing enough grout for your entire tiling job, ask the home center or tile supply store for a few samples of Hydroment grout in colors that you like. Spread the grout onto a piece of scrap wood, and allow the product to dry for 24 hours. After drying, lay some tiles next to the grout and see how the two look alongside each other. Because grout can change color during the drying process, this gives you a better idea of how the product actually appears following installation.
If you choose a color and then decide you do not like it after installing the tile, you can still change the color. Fortunately, Hydroment is an unsealed cement-based type of grout, as changing colors for epoxy-based grouts is not possible. If the grout is not sealed, an experienced tile installer can use a variety of staining products to give the tile a more pleasing color. While staining grout can make up for a poor initial color choice, tile contractors charge extra for this time-consuming job.