Activity for Private User

My fiancé wants him and his groomsman to wear different superhero shirts under their tuxes but my worry is that the color of the undershirt will show through a white shirt.. Has anyone's fiancé's done this successfully??

Okay, so I ordered my invites with only the one outer envelope and of course the rsvp card envelope, but my question is how is the rsvp envelope supposed to be addressed? I want to buy a stamp with me and my fiancé's name and our address on it, but...