Transitioning is completely a personal choice for you to make. There is no right or wrong answer. If you have naturally dark brown hair, as in a 1-2 on the color scale, you may not notice too much of a difference from your original color when you use Hairprint® on the dyed hair. If your hair is in the 3-5 range, it will be noticeably darker than your original color. The actual color your dyed hair turns out largely depends on how long you've dyed your hair, and how much damage has been done to the internal structure of the hair. The more damage that has been done to your hair, the darker it will be. You should assume your chemically-treated hair could turn black. If you're fine with potentially having the dyed hair turn black, then you don't need to transition, and you can jump right in to using Hairprint® on your entire head!
Please note: Your dyed hair will remain the dark color for the entire time you use Hairprint® because Hairprint® cannot reverse the damage done by chemical dyes. You will notice that as your new hair grows in, it will be much healthier and stronger than the chemically-dyed hair at your roots. Eventually as you continue to cut off the chemically-treated hair, you're going to end up with a healthy head of hair, free of damage and grays.