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)
This may be addressed directly in the Talmud. Menachot 40a states:
תנו רבנן סדין בציצית ב"ש פוטרין וב"ה מחייבין והלכה כדברי ב"ה א"ר אליעזר ב"ר צדוק והלא כל המטיל תכלת בירושלים אינו אלא מן המתמיהין אמר רבי א"כ למה אסרוה לפי שאין בקיאין אמר ליה רבא בר רב חנא לרבא ולרמו בי עשרה ונפקו לשוקא ומפרסמא למילתא כל שכן דמתמהו עילון ולידרשא בפירקא גזירה משום קלא אילן ולא יהא אלא לבן
Our Rabbis taught: A linen garment is, according to Beth Shammai, exempt from zizith; but Beth Hillel declare it liable. The halachah is in accordance with Beth Hillel. R. Eliezer son of R. Zadok said, Is it not a fact that any one in Jerusalem who attaches blue threads [to his linen garment] causes amazement? Rabbi said, If that is so, why did they forbid it? Because people are not versed in the law. Raba son of R. Hanan said to Raba, Then let ten people insert it and let them go about in the market place and so the law will be made known to all! People will wonder at it all the more. Then let it be announced at the public lecture! — It is to be feared that people will use imitation blue. But it is no worse than if it were white!
As Rashi there explains:
צבע היא שדומה לתכלת ואי שרית של תכלת בסדין אתי למירמי צמר צבוע בקלא אילן והוי כלאים שלא במקום מצוה וקפריך מאי איכפת לן אי רמי קלא אילן לא יהא האי קלא אילן אלא לבן בעלמא כלומר צמר לבן האמרן לעיל אין לו תכלת מטיל לבן
[Kala ilan] is a dye that is is similar to techeilet, and if you permit techeilet with linen then one will come to use wool dyed with kala ilan and it will be kelaim in a non-mitzvah situation. And [the Talmud] asks, what do we care if if one uses kala ilan? Let that kala ilan be [considered] nothing other than regular white, meaning to say white wool of which it was said earlier: "if he has no techeilet he should afix white".
The Talmud eventually rejects this line of argument for other reasons, but it seems that it was taken for granted that "wrong" techeilet does not affect the status of the tzitzit as a whole.