If you really wanted to be creative use all white flowers and put a few of them in water with blue food coloring and the will turn a bright blue color.
There is a rose called Hypnose that pairs wonderfully with your colors. We have wonderful brown things to add into designs such as wire, fern curl, ribbon and curly willow to name a few. As for your tiffany blue, I've used tiny crystals into the center of roses that are the tiffany blue. They come in a spray form and can be used that way or cut apart and glued in. The best thing is to work with complimentry colors. The rose I'm refering to can be seen at www.eufloriaflowers.com