What's the Halacha?

Q: May one wear photogray glasses (whose lenses darken in the sun) on Shabbos?

ANSWER: Yes, it is permitted to wear such glasses. Even though they change colors and thus pose a sha’ala of tzoveya (dyeing), poskim permit using them on Shabbos due to a combination of factors.

(כללים מלאכת צובע התירים פרק ב‘, סעיף ה‘ דוגמא 2)