My 4th gen was white, and my 5th gen is gray. White pretty much always looks clean, even if it's coated in a layer of dust, and it's also easier to wash. With the gray, and especially the 5th gen, there are a LOT of places for water to hide after you wash it -- especially the front end, side mirrors, and wiper for the rear window. If you don't get all those spots perfectly dry before driving it, you'll get all sorts of wonderful water streaks down the side/back of your truck. With white, you would never see them. Also, as others have mentioned, gray will show every little scratch or nick. If your wife's finger nails have any length to them, they might hit the paint under the door handle, and scratch it up.
Overall, my favorite color is gray, second favorite is silver, and white comes in at #3. They're all very good looking though!