As the ingredient list/instructions state you cook the pasta first The separate out the pasta (I have one plain added olive oil so the color does not transfer to those noodles) and color the blue and red in separate bags. You don’t need to rinse the noodles, but if you feel there is excess liquid you can blot the noodles or rinse if needed.
How long do you leave them in the color, until the desired color is achieved. Take a noodle out and see if you like the color. The color does not transfer if the noodles are not overly wet, hence why you add olive oil to the plain noodles. As you can see in the photos the colors stayed to themselves.

thanks for the great idea!

Of course, use any shape pasta you’d like.