Yes, flies can see green light.
Flies, like many insects, possess a visual system different from humans. Their vision is based primarily on two types of visual pigments. One of these pigments is highly sensitive to green and yellow light, absorbing light around the 550 nm wavelength. The other pigment is sensitive to blue and ultraviolet light, absorbing light below 480 nm. This means that flies are capable of perceiving green light as part of their color spectrum. They do not see red.
Therefore, flies perceive green light because they possess a visual pigment that absorbs this wavelength of light.
