Only white carnations can be used to change color using food dye. You will need one cup for each flower as well as food dye. A sharp knife or small cutting shears will be needed to properly cut the flowers so they can absorb the dye.
Each cup should be filled up halfway with about 30 drops of food coloring. The more drops used the bolder the color will be. The flower will need to be cut at an angle so that it can absorb the water. Once cut, it is important to quickly place it in the water. You also can cut the stem while it is under water to prevent air bubbles.
To have a single flower to have two colors the flower will need to absorb the two colors at the some time. This can be done by placing two cups side by side with two different colored dyes. The stem should be cut directly in half on the bottom. Each side should be placed in each cup allowing it to absorb the two different colors.