First you will need to start off with white roses, as many as you want though you will have to make them one at a time.
Next you need to split the stem using scissors. Split it into the number of different colors you want it to have.
Now you need to put a couple of drops of food coloring into different containers of water. Use as many colors as you want. The more food coloring you use, the darker and more concentrated the color will be on the rose. I used "neon" colors so it would be brighter.
Carefully place each part of the stem into a different container. I suggest pouring the water into smaller containers as the containers will have to be very close to each other for this. each rose will have to have its own set of cups and colors. Sorry I dont have a picture for this :(
Your rose should start absorbing the colors now. My roses took a couple of weeks because they were still blossoms, but it will depend on the type of rose and how close it is to blooming.
After they became the right color for me, I took them out of their food coloring and moved them into a vase. Enjoy your colorful creation!