Rav Shmuel Wosner zt"l addresses this in Shevet HaLevi, cheilek dalet, siman 23, os 5. He says that going out in the sun in such glasses is not considered an act of tzoveya.
בענין המשקפים שבאור השמש נעשות כהות אם מותר ללכת בהם בשבת - לבי נוטה יותר שמותר. ובמק"א נחזק זה אי"ה בראיות
With regards to glasses that the light of the sun makes go dark; if it is permitted to go in them on Shabbos - my heart is more inclined to permit it, and in another place we will strengthen this with proofs.
Rav Pesach Eliyahu Falk zt"l in Mechazeh Eliyahu, siman 65 (2nd paragraph in left column) brings this topic when talking about the halachic nature of thermometers and whether that also is a concern of tzoveya on Shabbos when taking a temperature reading. He brings the teshuva from Rav Moshe Feinstein (noted by @Shalom) which can be found in Igros Moshe, OC cheilek 3, siman 45 and says that there, Rav Moshe ruled that the blackness rises within the thickness of the glass and that there is no colour change fading at all but rather it is like coloured paper that sits behind the glass. However, he does question this as he asks that when the colour darkens/tints/fades there must be some form of tzoveya. He therefore concludes that it must only be tzoveyah derabbanan as the colourisation doesn't stay forever and that would perhaps be means to permit it.
Rav Shlomo Zalman Auerbach zt"l is also in the camp to permit such glasses. He refers to it in a footnote in Shemiras Shabbos Kehilchaso, Vol. 1, 18:18 (photo below of the English edition)