Line a large cookie sheet with parchment paper and set it aside.
Add about 1 cup of dry rigatoni pasta to a zip-lock bag. Pour in 1 teaspoon of rubbing alcohol and add about 20 drops of food coloring. Zip the bag closed and gently shake it around, using your hands to move the pasta so the color coats all sides of the noodles. Repeat this step for each color you want to make.
Open the bag and dump the colored pasta onto your parchment-lined baking sheet, spreading the pieces out so they are not touching. Let the pasta sit and dry for about 30 minutes.
After the pasta is fully dry, you are ready to turn it into a necklace. Cut a piece of yarn to the length you want. Slide a plastic needle onto one end of the yarn to make threading easier.
Start stringing the pasta onto the yarn, leaving some extra space at each end for tying. Alternate colors as you string the pasta. When you are done adding noodles, tie the ends of the yarn together. Your pasta necklace is ready to wear or share.