Welcome to our little playground, where the drinking fountains run yellow (muahahaha!)
Don't leave the sandbox though, or you might encounter the wrath of the almighty "PEE IS BAD" horde!
I have read in a few different places that it's OK to continue UT even while menstruating. Even if a little, uhh, "menstruation fluid", happens to get mixed in, it shouldn't hurt you any, even if it does seem a little gross...
Hope to see ya around :)