Get some samples or use the color chart as suggested. Whatever you do, don't make the decision on the color. That decision HAS to be the client's. I have clients sign a form stating they have chosen the color and acknowledging that they understand once the color is down, they own it. This is why I always do demos for color seal jobs. I think I adopted the form from the Grout Perfect marketing cd.
With regard to white color seal, it's fine as long as the client maintains the floor; wipes up spills, vacuums, and mops with a neutral cleaner. Their concern is also an opportunity to sell them on a yearly cleaning which extends the warranty (if you provide one) for an additional year.