Let's say I use the pretty much disproven Techelet (Radzyner) : is my Tzitzit completely Pasul? I think according to the Arizal it isn't. Does anyone disagree?
If you honestly believe that you are wearing true tekhelet then you are not in violation of the Gemara (BM 61b). If your tekhelet turns out to be false tekhelet, then you will have only fulfilled the mitzvah of tzitzit but not the aspect of tekhelet, as the Gemara (Men. 40a) explains is the case for one who unwittingly wore kela ilan - see my article "False Tekhelet": http://tekhelet.com/pdf/false.pdf
According to the Rambam, your tzizit can be any color really. The only thing they can't be is either all techelet, or techelet made from indidgo plants. (Some read this to mean any plants)
Since the Radzyner are made from animals and inorganic material but not plants, then this is not a problem.
I have heard some people say that you should put a bit of the dye on your clothing so that the strings are the same color as your garment, to fulfill the words of the Rambam properly. But I have also heard in the name of Rav Shachter, that really you can have any color on your tzizit at all regardles of the garment. As long as they are not all the same color (save white) and that they are not made from indigo.
However, you are not fulfilling the mitzvah of tzizit with lavan and Techelet when you have non-techelet dye on your tzizit.
According to the Rambam, the tzitzit is passul if you use the wrong blue-dye for the techelet. (See my post here: https://judaism.stackexchange.com/a/8913/702)