Fill the bowl with cold water and submerge the tips of the carnation stems in the water. While the stem tips are under water, use kitchen shears to cut the bottom 2 inches of the stems off. Cut the stems at a 45-degree angle for best results.
Pour approximately one cup of cool water into each jar (one jar for each color desired).
Add the food coloring to the water. If using liquid food coloring, add at least 30 drops into each jar. If using paste food coloring, add approximately 1/2 tsp. Mix the food colorings until they are completely incorporated.
Place the carnations into the colored-water jars. Make sure the tips of the stems are completely submerged at least 3 inches under the surface of the colored water.
Place the jars in a safe place and watch the coloring process, if desired. Color may appear in the petals in as little as 30 minutes, but timing will vary. After 24 hours, all of the color developing will be finished.
Remove the carnations from the colored water, rinse the stem tips under running water, and place them in plain water to enjoy.