SunnySunnybee: The purpose of the cummerbund, or vest, is to cover the waistband of the pants, and the working parts of the shirt. An evening formal shirt, which is worn with a tuxedo, is designed with a decorated bib, which is a rectangular, or sometimes u shaped, piece of fabric sewn onto the front of he shirt. This decorates the shirt for a formal occasion, as well as the diuble layer creating a pristine, stark white, avoiding any translucence in the shirt front. A white v shape of shirt, dramatically contrasts the black jacket, framed by the silk faced lapels of he jacket, drawing the eye up to the face, which is dramatically underlined by the bow tie. because the jacket can splay open below its buttoning point, especially when one puts his hands in his pockets, a white triangle of shirt can be shown below the button, immediately drawing the eye to the navel, and crotch. For this reason, a waist covering, which is either a low cut waistcoat/vest, which is totally hidden wgen the jacket is closed, is worn to cover the bottom of the shirt, and the waistband of the pants. This covers the working parts of the shirt and pants, which are incongruous with formal attire, and also maintains the unbroken line of black, that gives a man height, athleticism, and elegance, in evening lighting conditions. For this reason, black is the traditional, most correct, and best choice. Classic alternatives are more suited to less formal occasions, but they are very dark, rich, and as close to black as possible. Very dark burgundy/maroon, green, and plum, are the most traditional choices for going away from black, and are best as cummerbunds. A properly cut formal vest in these colours would have to be custom made, or, maybe, found vintage.
I would stick with black, self tie bow ties (look better, not hard to learn to tie, and you can buy them for $15 from http://www.thetiebar.com)
Before ordering, I would read http://www.theblacktieguide.com . You may choose not to follow the traditions, but this way you will be making a conscious choice that you want to, because of what you like best.