In the garden carnations are usually white or pink, but at the florist they are available in every color of the rainbow. Florists do not have access to special varieties that the average gardener doesn't--they actually dye the carnations to the desired color for the particular arrangement. You can emulate this process at home with your garden carnations using food dye. This allows you to alter your carnations so they match the other flowers in your arrangements and bouquets.
Fill a vase with lukewarm water. Add a floral preservative, available at florist shops, to the water and mix it in thoroughly. Add food coloring until the water reaches the desired shade.
Hold the stem of the carnation under running water from a faucet. Cut at least 1 inch off the bottom of the stem at a 45 degree angle. The water running over the stem as you cut prevents air pockets from entering the stem, so it is less likely to wilt.
Place the carnation into the prepared vase immediately after trimming the end. Set the vase in a cool room in bright, indirect sunlight. The dyed water is taken in by the carnation's stem then dyes the petals as it moves through the flower's vascular system.
Check the carnation every 12 to 24 hours. Add it to your floral arrangement once the petals of the carnation reach the desired color.