Fill each needle with one color of full-strength food coloring. You will need as many needles as you have colors to dye. Use standard food coloring available in grocery stores, or find neon colors in confectionery or craft stores. Needles are available from local pharmacies.
Grasp the rose by its stem, pulling it gently away from the bush. Use heavy-duty work gloves when handling thorny rose stems.
Insert the needle directly into the stem, with the tip facing the flower, about 6 inches beneath the flower. Inject the dye into the stem. Be careful not to insert the needle through the other side of the stem or you will waste your dye.
Inject additional colors of dye in the stem for a tie-dyed effect by creating a circle of injection sites around the stem.
Refill the needle with the same color dye to inject additional roses.
Water the roses according to your usual routine. As the water is absorbed, it will push the dye up through the stem and into the flower.
Allow about one week for the colors to be absorbed up into the flower head.