Yeah you're supposed to wear a plain white tee to a Gwar show so you have evidence of all the violence. Although the "blood" is actually all sorts of weird colors, one time I saw them and my shirt came out like blue/pink/purple.
hahah! no wonder there were so many kids wearing white shirts. I was sitting by the merch table, and it was pretty funny watching all these kids from the front walk back to the bathroom, looking like they suffered from a fruit juice explosion. they put on an entertaining show, that's for sure.