A cummerbund is typically worn with the pleats facing up. This traditional style detail is intended to catch any crumbs or spills that may occur during formal events.
NO!!! At best, this would look like a black suit worn with a purple tie. More likely, it would simply look shiny and ridiculous, only a small step up from the powder-blue/ruffled shirt style of the 1970s. The one lesson we have learned from the history of the tuxedo is that non-traditional, colorful accessories are never a good idea. YES!! A lot of people are ditching the cumberbunn and going with a vest for 2011. You might try that instead. I know of someone who wore a purple tie with a tux to a prom and it looked cool. A lot of guys are matching their date's dresses. Google search images and you'll see!