Wear an aqua blue top. To really get your costume looking right, try to get an aqua-blue hooded sweatshirt, t-shirt, or tank-top to turn into your Rainbow Dash costume. You don't really need to do anything to the shirt to make a costume out of it, just make sure it's the right color.
Kraft Vegemite Yeast Spread is a dark brown Australian food paste made from leftover brewers' yeast extract with various vegetable and spice additives developed by Cyril P. Callister in Melbourne, Victoria, in 1922.
Marmite was invented in the late 19th century when Justus von Liebig a scientist, found out that brewer's yeast could be bottled and eaten. http://en.wikipedia.org/wiki/Marmite. Vegemite is also made from brewer's yeast. Vegemite first appeared on the shopping shelves in 1923.