Thin-film interference occurs when light strikes a thin layer of transparent material, causing reflections from both the upper and lower interfaces. These reflected waves recombine and interfere constructively or destructively depending on the film's thickness, its refractive index, and the light's wavelength. This mechanism is the foundation of almost all optical coatings, including anti-reflective layers, dichroic mirrors, and narrow-bandpass filters.
The green tint on that lens is just thin-film interference from the broadband anti-reflection coating.
The thickness of the film is usually engineered to be a precise fraction of the target wavelength, most commonly a quarter-wave, to maximize destructive interference for reflections.
Related terms
AR coating
Antireflection coating: thin dielectric layers that cut surface reflections from about 4 percent to a fraction of a percent.
Antireflective
Treated to minimize the bouncing of light off an optical surface.
Etalon
A pair of parallel reflecting surfaces that transmits a comb of sharp frequency peaks, used to select or measure wavelengths.