I really like iron out--it does take out the color of the embroidered (did I spell that right???) label on pants (like the easton E that is now white on my son's pants).
I also learned from some wonderful person here to take the pants to the car wash and use the power washer on them when they are really bad.
Between those two approaches, I've had pretty good luck with the clay stuff and brick dust. tigermom--glad the soap worked, I may have to try that someday!