I know the regular minhagim, I do Raavad. My question was regarding “In other words you should tie on white tzitzit strings and then wind a blue string around the white strings.”

If you look at the tzitzit strings hanging down you see eight, but they are really four strings folded in half where they are inserted into the hole.

According to Rashi and Tosefot, you use two white and two blue. According to Raavad and the Gra you use three white and one blue. According to Rambam you use three white and one half blue/half white.

Depending on the tying custom, sometimes you will be wrapping one of the “eight” white strings around the core of seven, and sometimes you will be wrapping techeles around the core of seven.

Radzyn Techelet is sold with just a package of four blue strings, and you buy a regular package of white separately. That means you are going to have a total of four white strings left over.