Underpants

Dear Reverend,
The colour of underpants is always a big issue and many a Ninja has deliberated over the subject. The situation really will dictate the answer to this.
Are you conducting or officiating at the wedding?
Are you getting married?
Are you carrying out a hit at a wedding?
Underpants should always match the rest of your outfit unless you want the underpants themselves to make a statement or impact. There is nothing worse than having your cover in darkness blown by a pair of bright yellow glowing underpants still visible beneath your black hakama or chosen disguise. Likewise underpants are an important part of any ninja outfit, as it can be equally disruptive to have your tackle swaying freely under loose clothing whilst you try to scale a barbed wire fence.
My personal choice would be not to let the guests know you will be attending, which can be accomplished by simply not returning the RSVP invitation. However since you will have received a wedding invitation in the post (or even more stupidly sent out invitations to your own wedding with your address on) the happy couple (or invitees) now know where you live. You are therefore duty bound, of course to slip into the wedding under cover of darkness, cut the lights and slaughter everyone in the room in a wedding crasher festival of ninja death, before making a quick getaway over the rooftops.
So really it doesn't matter what colour underpants you wear as nobody (hopefully) will see them.