That fancy colored grout that you have your heart set on might have a little secret: it fades in the sunlight. These two photos show the same grout, applied at about the same time one year ago. As you can see, the color is almost gone on the table mosaic, although some traces of blue remain.
So, if you’re considering colored grout for an outdoor application, make sure that it won’t fade – or just stick to gray, since it’s less expensive and will stay gray pretty much forever.