We've hashed and rehashed the color deal many times before, here and on other boards. Bottom line is each show and sometimes each division (different breeds, junior, steers, heifers, open, futurities, etc...) within a show may have different rules regarding who can fit and what they may do. As has been pointed out here already, paint is not neccesarily (in fact, seldom) being used to change natural coloring, but to build and fill out the existing hair, and to cover the white left behind by strong adhesives. As the original poster said, there are no right or wrong answers to this, just opinions.
Speaking of opinions, I will say this much - having grown acustomed to being able to use paint, I really don't like fitting legs without it. Just personal opinion, and it probably has something to do with the hair quality on the particular Angus and Limousin cattle I usually help with, but I have a really hard time making a black leg look the way I like it using only the lighter adhesives that leave no white behind.