Buy a bouquet of white roses from a florist or supermarket, or if you're lucky enough to have your own rose garden, cut a few stems from a white rose bush.
Cut one inch off the bottom of the stems at a 45-degree angle. Cut each stem with a very sharp knife while the stem is under water, to avoid collapsing the xylem tubes or allowing air bubbles to block them, as these are the tubes that will carry the color to the petals.
Place the roses in a vase and add several inches of water, depending on the size of the vase.
Add a few drops of food coloring. The more food coloring you use, the stronger the color of the rose petals will be. If you want a more subdued pastel hue, use less food coloring. Use a separate vase for each different color.
Wait a few days for the roses to absorb the dyed water. When the petals transform into the color you want, remove the roses from the vase and empty out the dyed water. Then place the roses into a vase with fresh, clear water, or pluck the petals to scatter.