The team should be able to used whatever colors they want to put on their shirts as long as they are not doing gang related activities. Yeah, their school colors are orange and blue and most schools stick with their school colors on their t-shirts. Black is a color that can go with any color though, but the school administrators can't allow the gangs to use the two colors that is usually worn by everyone to be just for the gang. Making it seem only gang members can only wear blue and black, a lot of people wear blue jeans with some type of black shirt or shoes.
If the soccer team and volleyball team can win and look good doing it, they should be able to wear almost any color put together. Being concern about your school's safety is good in all but a situation like this is despicable. When the principal said that adding black to their color scheme is breaking tradition and sets a bad example for what they stand for, that really out of line and could be (to some people) a racist statement. And what do their school stand for?
Overall, this whole situation is ridiculous and can easily be handled without the school prohibiting the t-shirts. The principal should allow them to use those t-shirts with black and blue and if any problems occur with any type of gang related activity, they can prohibit the color. The team wants to look good to feel good and win.