I say keep all the t-shirts one color for everyone. So people can go to a show and notice the shirt, and know instantly it's someone from LPL, other than have a bunch of different colors. (Red is a good color choice in this case, black would be bad).
Also, I say make something more with the t-shirt. It's nice and simple, but it can be easily duplicated anywhere. I'm pretty sure Overkill was the one who made the shirt design. Again, nothing wrong with it, but I could go and make a million copies of it right now (even if I wasn't the one who created the logo to begin with. ). Overkill has WAY too much talent, and I'm sure he could make something even sicker than that! His posters prove it.
These things will sell like hotcakes!